Fix fatal error when configuring a PHP-CS-Fixer fixer

[TomasVotruba]

Fixes #44 and covers it in CI.

Cause

The bug does not need the scoped/prefixed release build - it reproduces on plain source, because composer.json has "replace": {"symfony/console": "*"}, so Symfony\Component\Console\Application is never installed.

Configuring a fixer whose option is deprecated hits ConfigurableFixerTrait::configure(), which calls PhpCsFixer\Console\Application::getMajorVersion(). That class extends the missing Symfony console Application, and PHP must resolve the parent class before the static call:

return ECSConfig::configure()
    ->withConfiguredRule(NullableTypeDeclarationForDefaultNullValueFixer::class, [
        'use_nullable_type_declaration' => false,
    ]);

PHP Fatal error:  Uncaught Error: Class "Symfony\Component\Console\Application" not found
  in vendor/friendsofphp/php-cs-fixer/src/Console/Application.php:51
#2 vendor/friendsofphp/php-cs-fixer/src/Fixer/ConfigurableFixerTrait.php(67): PHP_CodeSniffer\Autoload::load()
#3 src/Config/ECSConfig.php(391): ...NullableTypeDeclarationForDefaultNullValueFixer->configure()

In the released package the very same class is reported under its prefixed name, ECSPrefix202607\Symfony\Component\Console\Application.

Fix

Ship a declaration-only stub in /stubs, autoloaded via classmap. ECS never runs the php-cs-fixer console, so only the class declaration is needed.

php-scoper prefixes the stub along with everything else, so the release build gets ECSPrefix<YYYYMM>\Symfony\Component\Console\Application - exactly the name php-cs-fixer's Application extends there (verified by running php-scoper over /stubs with this repo config). stubs is added to the downgrade and scoping steps of the build workflow.

CI

New Configured Fixer workflow runs bin/ecs check with a configured fixer and asserts the run produces output instead of fatalling. It was red on the first commit of this PR and is green after the fix.

before:

PHP Fatal error: Uncaught Error: Class "Symfony\Component\Console\Application" not found

after:

1) build/nested/some_file.php
    ---------- begin diff ----------
@@ -1 +1,3 @@
-<?php  $x=1;
+<?php
+
+$x = 1;
    ----------- end diff -----------

Note on the failing Code Analysis job

PHPStan and Rector fail on this branch, but not because of it - composer.lock is gitignored, so CI always resolves the latest dev tools. On main, with today's versions, the same two failures appear:

• PHPStan: Multiple services of type Rector\TypePerfect\Reflection\MethodNodeAnalyser found (DI conflict inside rector/type-perfect)
• Rector: 6 files with readonly class changes proposed by the newer Rector, all untouched by this PR