[Testing] Allow a test case to resolve package versions from a standalone composer.json

[TomasVotruba]

A rule that implements ComposerPackageConstraintInterface is filtered out unless the bonded package is installed — RectorNodeTraverser::prepareNodeVisitors() applies ComposerPackageConstraintFilter unconditionally, so this hits the rule's own test run too. Every fixture then reports no change and the test fails.

That leaves an extension unable to test a rule bonded to a package it cannot add to require-dev. Concretely, in rector-symfony RedirectToRouteRector bonds to symfony/framework-bundle, which does not resolve against that repo's dev constraints at any major.

A test case can now name a standalone composer.json to read the versions from:

final class RedirectToRouteRectorTest extends AbstractRectorTestCase
{
    // ...

    protected function provideComposerJsonFilePath(): ?string
    {
        return __DIR__ . '/config/composer.json';
    }
}

{
    "require": {
        "symfony/framework-bundle": "^2.6"
    }
}

The require and require-dev constraints become the resolved versions, each one taking the lowest version it allows — ^2.6 resolves to 2.6.0.0. No vendor directory is read in this mode. An open constraint such as * has no lowest version and stays unresolved, same as a package that is not listed at all.

Notes

• InstalledPackageResolver gets an optional second constructor argument. Default behaviour is untouched: without it, versions still come from vendor/composer/installed.json with the composer.json constraints applied on top.
• The lower-bound logic is extracted from matchConstraintVersion() into resolveConstraintLowestVersion() and shared by both modes.
• changeComposerJsonFilePath() exists because ComposerPackageConstraintFilter keeps the first resolver it is handed for the whole process. The test case binds the resolver as a singleton once, then re-points it per test case, so a custom composer.json cannot leak into the next one. Re-binding the container entry instead would leave the filter holding a stale instance.

Verified against rector-symfony: with the rule bonded and this branch in place, its suite is green at 584 tests, including the 7 RedirectToRouteRector cases that fail without it.

tests/Composer/InstalledPackageResolverTest covers the new mode and the re-point. The 32 failures in the full suite are present on main as well and are unrelated.