35637c64339145f2920db0b6aee2dd8717109e63  [JSC] Iterate Arrays without allocating a `JSArrayIterator`

Classified as not security-relevant.
Triage note: Introduces a fastArraySentinel iteration mode where the iterator is a sentinel and next is the index, a new op_iterator_close_check opcode, LLInt/baseline/DFG support, and operationIteratorNextFastArray. JSC iteration performance feature; the rhs->tempDestination move is a requirement of the new opcode, not a stated bug fix.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+4.87), security_assert (+6.47), null_guard (+2.59), msg_feature (-1.0), area:Source/JavaScriptCore/bytecode (+2.5), large_churn (-2.0)