Implement isPublicSet(), fix isVirtual(), add isVirtual to parity tests (P3 + P5)

[devin-ai-integration]

Summary

Implements two sub-tasks from #162 (PHP 8.3/8.4 parity meta-issue):

P3 (#165): isPublicSet() method

• Adds isPublicSet() to ReflectionProperty that returns true when the set visibility is explicitly public(set) and the main visibility is not already public
• Delegates to php-parser's isPublicSet() on the underlying Property/Param node
• Note: native PHP 8.4's \ReflectionProperty does not have isPublicSet(), so parity testing is done via standalone test with expected values

P5 (#167): isVirtual() in parity test getters

• Adds 'isVirtual' to the PHP 8.4 getters in getGettersToCheck() so the parity test compares output with native reflection

Bug fix: isVirtual() implementation

• Adding isVirtual to parity tests exposed an incorrect implementation
• Previous logic only checked byRef on hooks — now correctly detects backing store usage:
  • Short set hooks (set => expr) always use backing store → NOT virtual
  • Block-form hooks that reference $this->propertyName use backing store → NOT virtual
  • Uses NodeFinder to walk AST for $this->propertyName references in block-form hooks

Review & Testing Checklist for Human

• Verify isPublicSet() semantics match your expectations — since native PHP lacks this method, the behavior is defined by us (returns false for all valid PHP 8.4 code since public(set) can't widen beyond main visibility)
• Verify isVirtual() fix handles edge cases: short get-only hooks (virtual), short set hooks (not virtual), block set hooks with/without $this->prop reference
• Run vendor/bin/phpunit — all 11807 tests should pass with 0 failures

Notes

• PHPStan passes with 0 errors
• PHPUnit: 11807 tests, 12519 assertions, 0 failures (141 skipped, 6 incomplete — pre-existing)

Link to Devin session: https://app.devin.ai/sessions/9af7c65d163e48af819f6c20c039d99b
Requested by: @lisachenko

[devin-ai-integration]

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