Add BigInt64Array and BigUint64Array types

[TimothyGu]

See whatwg/webidl#936.

• BigInt64Array and BigUint64Array are introduced as keywords.
• The ArrayBufferView and BufferSource aliases now include BigInt64Array and BigUint64Array as part of the union.

Concretely, the only change that appears to be necessary is changing the bufferSourceTypes array here:

TypeScript-DOM-lib-generator/src/build/helpers.ts

Lines 4 to 17 in a0f3ac4

	export const bufferSourceTypes = new Set([
	"ArrayBuffer",
	"ArrayBufferView",
	"DataView",
	"Int8Array",
	"Uint8Array",
	"Int16Array",
	"Uint16Array",
	"Uint8ClampedArray",
	"Int32Array",
	"Uint32Array",
	"Float32Array",
	"Float64Array",
	]);