Language: fix consecutive ?: call-arg misbind (#15816)

[PurHur]

Summary

Fixes multi-arg calls where consecutive ?: operands were misbound to the innermost merge phi — e.g. pair(true ? 'yes' : 'no', false ? 1 : 2) evaluated as $b,$b instead of $a,$b.

• Recognize classic ?: merge blocks via mergeCfgBlockUsesTernaryBranchLiteralAssign() (arms assign to shared temp; php-src Zend/zend_compile.c).
• Map each dead inline call-arg temporary to the correct innermost phi slot in resolveNestedTernaryMergeCallArgSlot() before TYPE_ARG_SEND.

php-src reference

• Zend/zend_compile.c — call argument emission / ?: merge temporaries
• Zend/zend_execute.c — ZEND_CALL frame slots

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php test/repro/maintainer_gap_call_multiarg_ternary_misbind.php
php bin/vm.php test/repro/maintainer_gap_call_multiarg_ternary_misbind.php
php bin/jit.php test/repro/maintainer_gap_call_multiarg_ternary_misbind.php
vendor/bin/phpunit --filter call_multiarg_ternary_misbind'

Output (VM/JIT match Zend):

a=yes b=2
yes-2
string(5) "array"
int(14)

PHPUnit: OK (2 tests, 2 assertions) (VM + JIT compliance).

Closes #15816

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