Parallel OxiPNG improvements

- Refactor to work around Chromium's issue with postMessage queuing. https://bugs.chromium.org/p/chromium/issues/detail?id=1075645
 - Convert codec code to TypeScript.
 - Make separate parallel and non-parallel builds.
 - Switch to nightly Rust for OxiPNG to allow parallel builds (but also reuse it for regular builds to avoid installing two toolchains).

codecs/oxipng/pkg/squoosh_oxipng.d.ts

@@ -1,36 +1,21 @@
 /* tslint:disable */
 /* eslint-disable */
 /**
-* @returns {any}
-*/
-export function worker_initializer(): any;
-/**
-* @param {number} num
-*/
-export function start_main_thread(num: number): void;
-/**
-*/
-export function start_worker_thread(): void;
-/**
-* @param {Uint8Array} data
-* @param {number} level
-* @returns {Uint8Array}
+* @param {Uint8Array} data 
+* @param {number} level 
+* @returns {Uint8Array} 
 */
 export function optimise(data: Uint8Array, level: number): Uint8Array;
 
 export type InitInput = RequestInfo | URL | Response | BufferSource | WebAssembly.Module;
 
 export interface InitOutput {
-  readonly worker_initializer: () => number;
-  readonly start_main_thread: (a: number) => void;
-  readonly start_worker_thread: () => void;
+  readonly memory: WebAssembly.Memory;
   readonly optimise: (a: number, b: number, c: number, d: number) => void;
   readonly malloc: (a: number) => number;
   readonly free: (a: number) => void;
-  readonly __wbindgen_export_0: WebAssembly.Memory;
   readonly __wbindgen_malloc: (a: number) => number;
   readonly __wbindgen_free: (a: number, b: number) => void;
-  readonly __wbindgen_start: () => void;
 }
 
 /**
@@ -38,9 +23,8 @@ export interface InitOutput {
 * for everything else, calls `WebAssembly.instantiate` directly.
 *
 * @param {InitInput | Promise<InitInput>} module_or_path
-* @param {WebAssembly.Memory} maybe_memory
 *
 * @returns {Promise<InitOutput>}
 */
-export default function init (module_or_path?: InitInput | Promise<InitInput>, maybe_memory: WebAssembly.Memory): Promise<InitOutput>;
+export default function init (module_or_path?: InitInput | Promise<InitInput>): Promise<InitOutput>;