Introduce FileNode to handle file-level changes #31817

Job	Run time
PHPStan	1m 34s
Help and Version	23s
Compatible PHPStan versions	24s
Active Classes	22s
Commented Code	21s
Check before/after test fixture on no-changes	25s
Preload php-parser Order	19s
Composer Validate	25s
Check fixture classes are different to nodes	18s
Detect composer dependency issues	21s
Check no "*.php" files in rules Fixture directory	21s
PHP Linter	28s
Finalize classes	27s
Run with Space in Directory	18s
	6m 26s

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