0d6cf47c3b1211a20135cc74ae54768dbeb1aa93  [JSC] Vectorize `Array#indexOf` and `Array#includes` on long Int32 and Double arrays

Classified as not security-relevant.
Triage note: Refactors operationArrayIncludes/IndexOf Double into vectorized WTF::findDouble/find64BitLaneImpl with a threshold and new JIT operations; the added index>=length guards are self-consistent with the new path. Performance work, not a fix of a shipped bug.
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: security_assert (+3.0), bounds_guard (+3.25), null_guard (+2.59), msg_feature (-1.0), area:Source/JavaScriptCore/dfg (+2.5), large_churn (-2.0)