Language: unpack() enum offset — inline pack call-arg slot wiring (#8866)

[PurHur]

Summary

• Fixes unpack('i', pack('i', 1), E::A) when pack() is an inline middle argument: the nested pack EXEC_RETURN now feeds argument Php stdlib specs implementation #2 ($string) and the hoisted enum case feeds argument Stdlib: ceil, floor, intval and expanded PHPT specs #3 ($offset).
• Adds nestedFuncCallFeedsDeadInlineCallArg() guards so hoisted enum prelude logic does not steal the middle nested-FuncCall slot.
• Adds specialized compileUnpackInlinePackEnumOffsetCallArgSends() for the literal + inline pack + enum offset pattern.

Closes #8866

Root cause

php-cfg hoists pack() and E::A before unpack(). The enum prelude slot mapper treated every dead inline temp after a nested FuncCall as the enum fetch, so both unpack operands received E::A instead of pack result + enum.

Verification

php test/repro/maintainer_gap_unpack_enum_offset.php
# TypeError: unpack(): Argument #3 ($offset) must be of type int, E given

php bin/vm.php test/repro/maintainer_gap_unpack_enum_offset.php
# TypeError: unpack(): Argument #3 ($offset) must be of type int, E given

./script/phpunit.sh --filter 'unpack_enum_offset_typeerror|testUnpackInlinePackEnumOffsetCallArgSlots'
# OK (2 tests, 2 assertions)

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