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-parallel/oxipng.js

@@ -0,0 +1,174 @@
+
+let wasm;
+let memory;
+
+const heap = new Array(32).fill(undefined);
+
+heap.push(undefined, null, true, false);
+
+let heap_next = heap.length;
+
+function addHeapObject(obj) {
+    if (heap_next === heap.length) heap.push(heap.length + 1);
+    const idx = heap_next;
+    heap_next = heap[idx];
+
+    heap[idx] = obj;
+    return idx;
+}
+
+let cachedTextDecoder = new TextDecoder('utf-8', { ignoreBOM: true, fatal: true });
+
+cachedTextDecoder.decode();
+
+let cachegetUint8Memory0 = null;
+function getUint8Memory0() {
+    if (cachegetUint8Memory0 === null || cachegetUint8Memory0.buffer !== wasm.__wbindgen_export_0.buffer) {
+        cachegetUint8Memory0 = new Uint8Array(wasm.__wbindgen_export_0.buffer);
+    }
+    return cachegetUint8Memory0;
+}
+
+function getStringFromWasm0(ptr, len) {
+    return cachedTextDecoder.decode(getUint8Memory0().slice(ptr, ptr + len));
+}
+
+function getObject(idx) { return heap[idx]; }
+
+function dropObject(idx) {
+    if (idx < 36) return;
+    heap[idx] = heap_next;
+    heap_next = idx;
+}
+
+function takeObject(idx) {
+    const ret = getObject(idx);
+    dropObject(idx);
+    return ret;
+}
+/**
+* @returns {any}
+*/
+export function worker_initializer() {
+    var ret = wasm.worker_initializer();
+    return takeObject(ret);
+}
+
+/**
+* @param {number} num
+*/
+export function start_main_thread(num) {
+    wasm.start_main_thread(num);
+}
+
+/**
+*/
+export function start_worker_thread() {
+    wasm.start_worker_thread();
+}
+
+let WASM_VECTOR_LEN = 0;
+
+function passArray8ToWasm0(arg, malloc) {
+    const ptr = malloc(arg.length * 1);
+    getUint8Memory0().set(arg, ptr / 1);
+    WASM_VECTOR_LEN = arg.length;
+    return ptr;
+}
+
+let cachegetInt32Memory0 = null;
+function getInt32Memory0() {
+    if (cachegetInt32Memory0 === null || cachegetInt32Memory0.buffer !== wasm.__wbindgen_export_0.buffer) {
+        cachegetInt32Memory0 = new Int32Array(wasm.__wbindgen_export_0.buffer);
+    }
+    return cachegetInt32Memory0;
+}
+
+function getArrayU8FromWasm0(ptr, len) {
+    return getUint8Memory0().subarray(ptr / 1, ptr / 1 + len);
+}
+/**
+* @param {Uint8Array} data
+* @param {number} level
+* @returns {Uint8Array}
+*/
+export function optimise(data, level) {
+    var ptr0 = passArray8ToWasm0(data, wasm.__wbindgen_malloc);
+    var len0 = WASM_VECTOR_LEN;
+    wasm.optimise(8, ptr0, len0, level);
+    var r0 = getInt32Memory0()[8 / 4 + 0];
+    var r1 = getInt32Memory0()[8 / 4 + 1];
+    var v1 = getArrayU8FromWasm0(r0, r1).slice();
+    wasm.__wbindgen_free(r0, r1 * 1);
+    return v1;
+}
+
+async function load(module, imports, maybe_memory) {
+    if (typeof Response === 'function' && module instanceof Response) {
+        memory = imports.wbg.memory = new WebAssembly.Memory({initial:17,maximum:16384,shared:true});
+        if (typeof WebAssembly.instantiateStreaming === 'function') {
+            try {
+                return await WebAssembly.instantiateStreaming(module, imports);
+
+            } catch (e) {
+                if (module.headers.get('Content-Type') != 'application/wasm') {
+                    console.warn("`WebAssembly.instantiateStreaming` failed because your server does not serve wasm with `application/wasm` MIME type. Falling back to `WebAssembly.instantiate` which is slower. Original error:\n", e);
+
+                } else {
+                    throw e;
+                }
+            }
+        }
+
+        const bytes = await module.arrayBuffer();
+        return await WebAssembly.instantiate(bytes, imports);
+
+    } else {
+        memory = imports.wbg.memory = maybe_memory;
+        const instance = await WebAssembly.instantiate(module, imports);
+
+        if (instance instanceof WebAssembly.Instance) {
+            return { instance, module };
+
+        } else {
+            return instance;
+        }
+    }
+}
+
+async function init(input, maybe_memory) {
+    if (typeof input === 'undefined') {
+        input = import.meta.url.replace(/\.js$/, '_bg.wasm');
+    }
+    const imports = {};
+    imports.wbg = {};
+    imports.wbg.__wbindgen_module = function() {
+        var ret = init.__wbindgen_wasm_module;
+        return addHeapObject(ret);
+    };
+    imports.wbg.__wbindgen_memory = function() {
+        var ret = wasm.__wbindgen_export_0;
+        return addHeapObject(ret);
+    };
+    imports.wbg.__wbg_of_9335425aa94288f5 = function(arg0, arg1) {
+        var ret = Array.of(takeObject(arg0), takeObject(arg1));
+        return addHeapObject(ret);
+    };
+    imports.wbg.__wbindgen_throw = function(arg0, arg1) {
+        throw new Error(getStringFromWasm0(arg0, arg1));
+    };
+
+    if (typeof input === 'string' || (typeof Request === 'function' && input instanceof Request) || (typeof URL === 'function' && input instanceof URL)) {
+        input = fetch(input);
+    }
+
+    const { instance, module } = await load(await input, imports, maybe_memory);
+
+    wasm = instance.exports;
+    init.__wbindgen_wasm_module = module;
+    wasm.__wbindgen_start();
+    return wasm;
+}
+
+export default init;
+