Language: by-reference parameters JIT/AOT lowering (#3161)

[PurHur]

Summary

• Implements JIT lowering for by-reference function parameters (function f(&$x)), closing the gap after VM work in Language: Reference assignment and by-ref parameters #140.
• Callee formals bind to caller __value__* storage via valueBoxAliasPtr (same model as closure use (&$x) / foreach by-ref).
• Call sites promote native scalars to boxed lvalues when needed; Helper::loadValue and assignOperand read/write through aliases.

php-src reference

• Zend/zend_compile.c — zend_compile_param() by_ref
• Zend/zend_execute.c — ZVAL_MAKE_REF, argument binding by reference

Verification

# VM (passes)
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && ./vendor/bin/phpunit --filter ref_param test/compliance/VMTest.php'

# JIT compliance (added ref_param_jit.phpt)
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && ./vendor/bin/phpunit --filter ref_param_jit test/compliance/JITTest.php'

# Repro
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php -r "function inc(&\$n){\$n++;} \$x=1; inc(\$x); echo \$x;"'

Note: This harness Docker image currently segfaults on bin/jit.php MCJIT execute even for echo 42 (exit 139); the ref-param repro compiles without the prior Unsupported cast … __value__* / valuePtrFromVariable failures. Full JIT execute green needs the LLVM 9 dev image / make test path from script/ci-local.sh.

Test plan

• VM compliance ref_param.phpt
• JIT compliance case ref_param_jit.phpt added
• docs/capabilities-syntax.md — by-ref row JIT/AOT yes
• make test / ./script/ci-local.sh --filter ref_param on LLVM host when available

Closes #3161

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