BigInt typed arrays

Date: 2026-04-20 Area: runtime Pull Request: #365

BigInt64Array/BigUint64Array (ES2020). Adds the two BigInt-typed array constructors, completing typed array coverage. Elements are BigInt values; setting non-BigInt throws TypeError. All prototype methods (sort, indexOf, includes, fill, find, map, filter, reduce, etc.) handle BigInt kinds correctly. built-ins-binary-data.md.