Clone boxed BigInt values in structuredClone - #58211

Summary:

The structured-clone polyfill handles boxed Boolean, Number, and String objects but returns a plain empty object for boxed BigInt. Capture the built-in BigInt valueOf, read the internal primitive without user overrides, clone the wrapper through that value, and register it in clone memory.

Fixes #58210.

Changelog:

[GENERAL] [FIXED] - Preserve boxed BigInt values in structuredClone without user coercion.

Test Plan:

• Exact Hermes baseline failed the BigInt-wrapper assertion.
• Final regression shadows the source wrapper's valueOf with a throwing function; the clone is distinct, remains a BigInt wrapper, and returns 1n, matching native structuredClone.
• Fixed focused Fantom suite: 32/32 passed.
• Fresh yarn flow-check: 0 errors.
• Targeted ESLint, Prettier, and git diff --check passed.

No UI change; screenshots are not applicable.