fix(symfony): use StrictUnifiedDiffOutputBuilder in api:upgrade-filter

[mislavjakopovic]

Q	A
Branch?	5.0
Tickets	none
PRs	Preparation for #8537
License	MIT
Doc PR	n/a

Currently our UpgradeApiFilterCommand::diff() builds the dry-run diff with SebastianBergmann\Diff\Output\UnifiedDiffOutputBuilder, which no longer exists in sebastian/diff: "^9".

Why we need this for PHPUnit 13:

• sebastian/diff 9.0.0 removed UnifiedDiffOutputBuilder and AbstractChunkOutputBuilder, and suggests to "use StrictUnifiedDiffOutputBuilder instead" (Remove UnifiedDiffOutputBuilder and AbstractChunkOutputBuilder sebastianbergmann/diff#157).
• PHPUnit pins the sebastian/diff major: 11.5 requires ^6.0.2, 12.5 ^7.0.1, 13.1 ^8.3.0, and 13.2.0 switched to ^9.0 (13.3.4: ^9.0.1), see the composer.json of those tags. So every install of PHPUnit 13.2 or newer comes with sebastian/diff 9.
• On such an install the dry-run dies with Error: Class "SebastianBergmann\Diff\Output\UnifiedDiffOutputBuilder" not found as soon as it finds a resource to upgrade, and PHPStan reports the two lines. That is what happened on the first run of chore: allow phpunit ^13.0 #8537 once the constraint allowed PHPUnit 13:
  https://github.com/api-platform/core/actions/runs/35087612230/job/104766045721 (Instantiated class SebastianBergmann\Diff\Output\UnifiedDiffOutputBuilder not found
  at UpgradeApiFilterCommand.php:215).

The proposed fix in this pull request is a replacement from UnifiedDiffOutputBuilder to StrictUnifiedDiffOutputBuilder with fromFile/toFile, which has existed since sebastian/diff 3.0.0, as it emits the same --- original / +++ upgraded header, and it produces identical output on 6.0.2, 7.0.1, 8.x and 9.0.1.

It is the builder php-cs-fixer uses across ^4.0.6 || ^5.1.1 || ^6.0.2 || ^7.0 || ^8.0 || ^9.0 (src/Differ/UnifiedDiffer.php), and the one PHPUnit 13 (src/Util/DifferBuilder.php) and sebastian/comparator 8 (ComparisonFailure) use themselves.

The only visible change is that dry-run hunks carry real line ranges instead of @@ @@.

About added test:

I've had some problems with codecov:patch while preparing this pull request. It failed on 0% change:
https://app.codecov.io/gh/api-platform/core/pull/8559?dropdown=coverage&src=pr&el=h1

After exploring for several hours I'm still not 100% about what happened there but it looks like this dry-run path of the command had no test; the only CI job running the codemod (upgrade-filter) runs with coverage disabled and exercises --force on a fixture app with nothing to upgrade, so diff() was never executed and the command had no coverage at all.

codecov/patch "only measured lines adjusted in the pull request" against the base coverage (https://docs.codecov.com/docs/commit-status#patch-status), which is why I suspect the small two-lined fix alone scored 0% (https://github.com/api-platform/core/pull/8559/checks?check_run_id=106508255530).

Again, these are just my speculations - after adding a test the issue was gone. I was not able to find any previous precedents in pull requests which would either confirm or deny above and given I don't have experience with Codecovas service the only thing I could done to resolve this is a to write a test that should help us avoid issues with this exact problem and command in the future.

If this looks weird to maintainers I would appreciate someone looking it and giving feedback on it.

This pull request is part of several fixes needed to enable PHPUnit 13 support in PR #8537.