WebAssembly BigInt<->i64 conversion in JS API

With the changes in this repository, BigInts have support for bidirectionally converting to 64-bit integer WebAssembly values, which appears as

• Parameters and return values to exported WebAssembly functions
• Parameters and return values to host functions
• Imported and exported globals

BigInts can be read or written from WebAssembly memory using the BigInt proposal's BigInt64Array or BigUint64Array; no additional support is needed.

Design issue