Improve interpreted Test262 parity for Array and String

[nickna]

Summary

• generalize Array.prototype receivers and preserve callback receiver identity
• surface guest TypeErrors for invalid Array callbacks and distinguish arguments objects from arrays
• implement JavaScript coercion and optional-argument semantics across String character, search, padding, normalization, and code-point methods

Results

• interpreted Test262 passes: 6077 -> 6592 (+515)
• failures: 3098 -> 2770 (-328)
• runtime errors: 1317 -> 1130 (-187)
• baseline regressions: 0

Validation

• focused cross-mode Test262 parity pins: 49 passing cases across the five batches
• nearby SharpTS tests: Array batch 197/197; arguments batch 199/199; String batches 167/167
• complete interpreted Test262 baseline sweep: 11,384 cases, 515 new passes, 0 regressions

Part of #1279.