php-in-php: move StringVarExportUserScriptLlvm to JitVarExportKernel (#19430)

[PurHur]

Summary

• Move user-script / deferred AOT __compiler_var_export bridge from lib/JIT/Builtin/StringVarExportUserScriptLlvm.php into ext/standard/JitVarExportKernel.php (kernel-quarantine pattern php-in-php: move StringHtmlspecialcharsUserScriptLlvm → JitHtmlspecialcharsKernel in ext/standard (#1492) #19389/php-in-php: move PregMatchUserScriptLlvm stubs → JitPregMatchKernel in ext/standard (#1492) #19399).
• StringVarExport defer path now calls JitVarExportKernel::implement; embed/full path unchanged via VarExportJitHelper.
• Spine + inventory updated; shrink tests guard the move.

LOC: deleted lib/JIT/Builtin/StringVarExportUserScriptLlvm.php (~87 LOC); added ext/standard/JitVarExportKernel.php (net shrink of JIT-builtin surface).

Closes #19430

Test plan

• ./script/phpunit.sh --filter VarExportRuntimeShrinkTest → OK (4 tests)
• ./script/phpunit.sh test/compliance/VarExportVMTest.php → OK (5)
• ./script/phpunit.sh test/compliance/VarExportJITTest.php → OK (2)
• php script/bootstrap-inventory.php --check → OK 5051/5051
• php script/check-selfhost-spine-coverage-sync.php → OK
• make bootstrap-selfhost-vm-driver-execute-probe → OK

Note: standalone var_export AOT currently segfaults after c:main_before_php on master as well (embed + PHP_COMPILER_AOT_USER_SCRIPT); HelloWorld AOT OK. Not introduced by this quarantine.

Verification transcript

OK (4 tests, 19 assertions)  # VarExportRuntimeShrinkTest
OK (5 tests, 5 assertions)   # VarExportVMTest
OK (2 tests, 2 assertions)   # VarExportJITTest
OK 5051/5051
check-selfhost-spine-coverage-sync: OK
bootstrap-selfhost-vm-driver-execute-probe: OK

Made with Cursor