php-in-php: route similar_text() JIT through SimilarTextJitHelper PHP (#9731)

[PurHur]

Summary

• Add ext/standard/SimilarTextJitHelper.php delegating to VmString::similar_text() (php-src ext/standard/string.c).
• Move JIT/AOT phpc_similar_text bridge into StringSimilarText.php; shrink StringSimilarTextJit.php from 420 → 17 lines (96% LLVM emitter removed — compat shim only).
• Add shrink + standalone inventory guards; wire SimilarTextJitHelper into self-host spine.

C runtime shrink

File	Before	After	Δ
lib/JIT/Builtin/StringSimilarTextJit.php	420	17	−403
lib/JIT/Builtin/StringSimilarText.php	23	123	+100 (thin bridge)
Net			−297 lines

Deleted LLVM symbols: __phpc_similar_str, __phpc_similar_char, hand-written phpc_similar_text Oliver loops.

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter SimilarText'
# OK (11 tests, 25 assertions)

make bootstrap-selfhost-vm-driver-execute-probe
# bootstrap-selfhost-vm-driver-execute-probe: OK

php script/check-selfhost-spine-coverage-sync.php
# check-selfhost-spine-coverage-sync: OK

Closes #9731

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