…(dunglas)

This PR was squashed before being merged into the 3.3-dev branch (closes #20509).

Discussion
----------

[Serializer] Allow to specify a single value in @groups

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #19374 (comment)
| License       | MIT
| Doc PR        | todo

Tiny DX improvement:

Before:

```php
use Symfony\Component\Serializer\Annotation\Groups;

class Product
{
    /**
     * @groups({"admins"})
     */
    public $itemsSold;
}
```

Now allowed:

```php
use Symfony\Component\Serializer\Annotation\Groups;

class Product
{
    /**
     * @groups("admins")
     */
    public $itemsSold;
}
```

Commits
-------

926aa48 [Serializer] Allow to specify a single value in @groups

…ps opt (dunglas)

This PR was merged into the 4.2-dev branch.

Discussion
----------

[Serializer] Allow to pass a single value for the groups opt

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets |  n/a
| License       | MIT
| Doc PR        | todo

Shortcut syntax similar to #20509 but for the context: allows to pass a string instead of an array of string in the serialization context when only one group if used.

Before:

```php
$serializer->serialize($foo, 'json', ['groups' => ['myGroup']];

/** @ApiResource(normalizationContext={"groups"={"myGroup"}}) */
```

After:

```php
$serializer->serialize($foo, 'json', ['groups' => 'myGroup'];

/** @ApiResource(normalizationContext={"groups"="myGroup") */
```

Commits
-------

5b39203 [Serializer] Allow to pass a single value for the groups opt

…(dunglas)

This PR was merged into the 3.4 branch.

Discussion
----------

[Serializer] Allow to specify a single value in @groups

symfony/symfony#20509

Commits
-------

99df65f [Serializer] Allow to specify a single value in @groups