php-in-php: route preg_* JIT embed through PregJitHelper (#9542)

[PurHur]

Summary

• Add ext/standard/PregJitHelper.php as SSOT over VmPregNative for embed JIT/AOT preg builtins
• Add lib/JIT/Builtin/PregMatchRuntime.php with LLVM bridges to compiled PHP helpers
• Shrink StringPregMatchJit.php to a 68-line dispatcher; quarantine pcre2 LLVM to StringPregMatchStandaloneLlvm.php (standalone AOT only)
• preg_replace_callback embed still uses a thin LLVM slice from standalone until callback ABI is PHP-hosted

Closes #9542

LLVM shrink

File	Before	After
StringPregMatchJit.php (embed dispatch)	~3250	68
pcre2 monolith	inline	StringPregMatchStandaloneLlvm.php (standalone only)

php-src reference

• ext/pcre/php_pcre.c — behavior via existing VmPregNative / VmPregMatches

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
vendor/bin/phpunit --filter "PregMatchRuntimeShrinkTest|PregExpandRuntimeShrinkTest|RuntimeShrinkCloseoutTest"
# OK (6+3 tests)

php bin/vm.php test/compliance/cases/stdlib/preg_match_basic.phpt
php bin/jit.php test/compliance/cases/stdlib/preg_match_basic.phpt
php bin/jit.php -r "var_export(preg_match(\"/(\d+)/\", \"abc123\", \$m)); echo PHP_EOL, \$m[1];"
# 1 / 1 / 1 / 123

for f in preg_match_flags_offset_jit.phpt preg_last_error_jit.phpt preg_replace_backref_jit.phpt preg_split_flags_jit.phpt; do
  php bin/jit.php test/compliance/cases/stdlib/$f
done
# all green

php script/check-selfhost-spine-coverage-sync.php
make bootstrap-selfhost-vm-driver-execute-probe
# OK
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