…errors on PHP 7.4 (alexpott)

This PR was squashed before being merged into the 3.4 branch (closes symfony#34097).

Discussion
----------

[Validator] Ensure numeric subpaths do not cause errors on PHP 7.4

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tickets       | Fix #... <!-- prefix each issue number with "Fix #", if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

Drupal is testing on PHP7.4 and hitting a problem with the line `if ('[' === $subPath[0]) {` because `$subPath` is not a string. We're already doing string casting in the method so we could do it once and be done. Note this is not a problem on the master branch / SF5 because of primitive typehinting.

Without this fix on PHP7.4 you see errors like...
```
1) Symfony\Component\Validator\Tests\Util\PropertyPathTest::testAppend with data set #5 ('0', 1, '0.1', 'Numeric subpaths do not cause...rrors.')
Trying to access array offset on value of type int
```

Commits
-------

6244a1e [Validator] Ensure numeric subpaths do not cause errors on PHP 7.4

This PR was merged into the 5.3-dev branch.

Discussion
----------

[Security] Added debug:firewall command

| Q             | A
| ------------- | ---
| Branch?       | 5.x
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       | Fix symfony#39321
| License       | MIT
| Doc PR        | symfony/symfony-docs#14982
| Tags | #SymfonyHackday

### Subtasks
- [x] Add list view (for use without arguments)
- [x] Add more information to list view
- [x] Add detail view (for use with `firewall` argument)
- [x] Add more information to detail view table
- [x] Add authenticators list
- [x] Add event listeners & events (copy from `debug:event-listener`)
- [x] Add `--include-listeners` option (default: false)
- [x] Add helptext
- [x] Add documentation

### Moved outside of current scope
- Add allowed badges

### Usage (and example output) for a list
`bin/console debug:firewall`

```
Firewalls
=========

 The following firewalls are defined:
 --------
  Name
 --------
  dev
  public
  main
 --------

 // To view details of a specific firewall, re-run this command with a firewall name. (e.g. debug:firewall
 // main)
```

### Usage (and example output) for details
`bin/console debug:firewall main`

```
Firewall "main"
===============

 ----------------------- ---------------------------------------------------
  Option                  Value
 ----------------------- ---------------------------------------------------
  Name                    main
  Context                 main
  Lazy                    Yes
  Stateless               No
  User Checker            security.user_checker
  Provider                security.user.provider.concrete.app_user_provider
  Entry Point             App\Security\LoginFormAuthenticator
  Access Denied URL
  Access Denied Handler
 ----------------------- ---------------------------------------------------

User switching
--------------

 ----------- ---------------------------------------------------
  Option      Value
 ----------- ---------------------------------------------------
  Parameter   test
  Provider    security.user.provider.concrete.app_user_provider
  User Role   ROLE_SWITCH_POSSIBLE
 ----------- ---------------------------------------------------

Event listeners for firewall "main"
===================================

"Symfony\Component\Security\Http\Event\LoginSuccessEvent" event
---------------------------------------------------------------

 ------- -------------------------------------------------------------------------------------------- ----------
  Order   Callable                                                                                     Priority
 ------- -------------------------------------------------------------------------------------------- ----------
  #1      Symfony\Component\Security\Http\EventListener\UserCheckerListener::postCheckCredentials()    256
  #2      Symfony\Component\Security\Http\EventListener\SessionStrategyListener::onSuccessfulLogin()   0
  #3      Symfony\Component\Security\Http\EventListener\RememberMeListener::onSuccessfulLogin()        0
  #4      App\Security\UpdateLastLogin::__invoke()                                                     0
  #5      Symfony\Component\Security\Http\EventListener\PasswordMigratingListener::onLoginSuccess()    0
 ------- -------------------------------------------------------------------------------------------- ----------

"Symfony\Component\Security\Http\Event\LogoutEvent" event
---------------------------------------------------------

 ------- ------------------------------------------------------------------------------------------- ----------
  Order   Callable                                                                                    Priority
 ------- ------------------------------------------------------------------------------------------- ----------
  #1      Symfony\Component\Security\Http\EventListener\DefaultLogoutListener::onLogout()             64
  #2      Symfony\Component\Security\Http\EventListener\SessionLogoutListener::onLogout()             0
  #3      Symfony\Component\Security\Http\EventListener\RememberMeLogoutListener::onLogout()          0
  #4      Symfony\Component\Security\Http\EventListener\CsrfTokenClearingLogoutListener::onLogout()   0
 ------- ------------------------------------------------------------------------------------------- ----------

"Symfony\Component\Security\Http\Event\CheckPassportEvent" event
----------------------------------------------------------------

 ------- ------------------------------------------------------------------------------------------ ----------
  Order   Callable                                                                                   Priority
 ------- ------------------------------------------------------------------------------------------ ----------
  #1      Symfony\Component\Security\Http\EventListener\LoginThrottlingListener::checkPassport()     2080
  #2      Symfony\Component\Security\Http\EventListener\UserProviderListener::checkPassport()        2048
  #3      Symfony\Component\Security\Http\EventListener\UserProviderListener::checkPassport()        1024
  #4      Symfony\Component\Security\Http\EventListener\CsrfProtectionListener::checkPassport()      512
  #5      Symfony\Component\Security\Http\EventListener\UserCheckerListener::preCheckCredentials()   256
  symfony#6      App\Security\DisallowBannedUsers::__invoke()                                               0
  symfony#7      Symfony\Component\Security\Http\EventListener\CheckCredentialsListener::checkPassport()    0
 ------- ------------------------------------------------------------------------------------------ ----------

"Symfony\Component\Security\Http\Event\LoginFailureEvent" event
---------------------------------------------------------------

 ------- ----------------------------------------------------------------------------------- ----------
  Order   Callable                                                                            Priority
 ------- ----------------------------------------------------------------------------------- ----------
  #1      Symfony\Component\Security\Http\EventListener\RememberMeListener::onFailedLogin()   0
 ------- ----------------------------------------------------------------------------------- ----------

Authenticators for firewall "main"
==================================

 // @todo: List authenticator information

```

Commits
-------

a9dea1d [Security] Added debug:firewall command