Replace NodeFinder with direct recursion in shouldInvalidateExpression()

[staabm]

The findFirst() call allocated a NodeTraverser + FirstFindingVisitor and paid the full visitor protocol (~4 calls per visited node) for every (stored expression, invalidated expression) pair that passes the substring pre-filter - about 2M visited nodes per analysed slice. A hand-rolled pre-order search with identical match semantics does one method call per node.

taken from 517cde7

before this PR:

➜  phpstan-src git:(2.2.x) ✗ php bin/phpstan clear-result-cache -q && time php -d memory_limit=450M bin/phpstan analyze src/Analyser -q
21.57s user 1.66s system 314% cpu 7.379 total
➜  phpstan-src git:(2.2.x) php bin/phpstan clear-result-cache -q && time php -d memory_limit=450M bin/phpstan analyze src/Analyser -q
21.34s user 1.61s system 320% cpu 7.150 total
➜  phpstan-src git:(2.2.x) php bin/phpstan clear-result-cache -q && time php -d memory_limit=450M bin/phpstan analyze src/Analyser -q
21.51s user 1.50s system 318% cpu 7.233 total

after this PR:

➜  phpstan-src git:(2.2.x) php bin/phpstan clear-result-cache -q && time php -d memory_limit=450M bin/phpstan analyze src/Analyser -q
20.45s user 1.57s system 327% cpu 6.714 total
➜  phpstan-src git:(2.2.x) php bin/phpstan clear-result-cache -q && time php -d memory_limit=450M bin/phpstan analyze src/Analyser -q
20.46s user 1.58s system 327% cpu 6.722 total
➜  phpstan-src git:(2.2.x) php bin/phpstan clear-result-cache -q && time php -d memory_limit=450M bin/phpstan analyze src/Analyser -q
20.52s user 1.54s system 324% cpu 6.797 total

[phpstan-bot]

This pull request has been marked as ready for review.