This PR was merged into the 3.4 branch.

Discussion
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[Intl] Add FallbackTrait for data generation

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #...   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

This is the last architectural change for the Intl data compilation. Promised.

It fixes de-duplicating a locale from its fallback locale. The problem is it uses a while-loop, comparing the locale to each fallback locale.

Given

- `root` (val=A)
  - `ur` (val=B)
    - `ur_IN` (val=A)

We have an edge case where a locale (ur_IN) override its fallback locale (ur), setting/restoring the value back to the root locale. This happens for the GMT format in the timezone bundle i know of ... in this case the `ur_IN` locale needs to write its own value.

The current approach is a while-loop comparing each fallback locale (ur, root) to the current locale (ur_IN). Eventually comparing `ur_IN <> root`, which causes a wrong diff, as such `ur_IN` falls back to `ur` providing the wrong value (val=B, where val=A is expected).

The new approach uses recursion so we only compare `ur <> ur_IN`, where `ur_IN` on itself is compared to `root`.

4.2) https://github.com/ro0NL/symfony/commit/e24d8e6
4.3) https://github.com/ro0NL/symfony/commit/31591d0

Commits
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36ddfd5 [Intl] Add FallbackTrait for data generation

This PR was merged into the 4.3 branch.

Discussion
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 [Intl] Revise timezone name generation

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no
| Tests pass?   | yes (inlcluding intl-data group)
| Fixed tickets | #...   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

This is the final polishing needed for #31294 :)

I've realized it's much easier to de-duplicate by processing fallback locales separate, and then only keep the diff compared to a specific locale. More or less the same approach `LocaleDataGenerator` already follows. I was trying to be clever and filter based on inheritance in a single process; bad idea.

Includes https://github.com/ro0NL/symfony/commit/31591d0 (ref #31432)

Commits
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bfdb4ed [Intl] Revise timezone name generation