php-in-php: route json_decode JIT through JsonDecodeJitHelper PHP (#9359)

[PurHur]

Summary

• Add ext/standard/JsonDecodeJitHelper.php as SSOT for runtime json_decode() / json_validate() / json_last_error* in compiled JIT modules (delegates to VmJsonFormat, VmJsonScanner, VmJson).
• Rewrite lib/JIT/Builtin/StringJsonDecode.php to thin LLVM bridges (pattern from #9267 encode / #9163 unserialize); standalone AOT still uses StringJsonDecodeJit (~2128 LOC LLVM quarantine).
• StringJsonDecode.php grows from 41 → ~230 lines of bridge glue; JIT decode path no longer calls StringJsonDecodeJit::implement() on embed builds.

php-src ref: ext/json/php_json.c — php_json_decode_ex, php_json_validate

C/LLVM shrink: JIT/normal __compiler_json_decode no longer emits StringJsonDecodeJit parser LLVM (~2.1k lines bypassed on embed path; monolith retained for standalone only).

Closes #9359

Test plan

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
./vendor/bin/phpunit --filter JsonDecodeRuntimeShrinkTest
./vendor/bin/phpunit --filter StringJsonDecodeRuntimeStandaloneTest
./vendor/bin/phpunit --filter "json_decode\.phpt|json_decode_jit|json_last_error" test/compliance/
php bin/vm.php -r "var_export(json_decode(\"{\\\"a\\\":1}\", true)); echo \"\n\";"
php bin/jit.php -r "var_export(json_decode(\"{\\\"a\\\":1}\", true)); echo \"\n\";"
'
make bootstrap-selfhost-vm-driver-execute-probe

Results (2026-06-26):

• JsonDecodeRuntimeShrinkTest — OK (3 tests)
• StringJsonDecodeRuntimeStandaloneTest — OK (3 tests)
• Compliance filter json_decode|json_last_error — OK (17 tests)
• VM/JIT repro json_decode('{"a":1}', true) — array ('a' => 1,)
• make bootstrap-selfhost-vm-driver-execute-probe — OK

Made with Cursor