Swap OptiPNG with OxiPNG

This makes building simpler and allows us to potentially use multithreading version in the future.

For now points to a custom fork of OxiPNG that enables WebAssembly support, as PR is still pending review.

codecs/oxipng/pkg/oxipng.js

@@ -0,0 +1,54 @@
+import * as wasm from './oxipng_bg.wasm';
+
+let cachegetUint8Memory = null;
+function getUint8Memory() {
+    if (cachegetUint8Memory === null || cachegetUint8Memory.buffer !== wasm.memory.buffer) {
+        cachegetUint8Memory = new Uint8Array(wasm.memory.buffer);
+    }
+    return cachegetUint8Memory;
+}
+
+let WASM_VECTOR_LEN = 0;
+
+function passArray8ToWasm(arg) {
+    const ptr = wasm.__wbindgen_malloc(arg.length * 1);
+    getUint8Memory().set(arg, ptr / 1);
+    WASM_VECTOR_LEN = arg.length;
+    return ptr;
+}
+
+let cachegetInt32Memory = null;
+function getInt32Memory() {
+    if (cachegetInt32Memory === null || cachegetInt32Memory.buffer !== wasm.memory.buffer) {
+        cachegetInt32Memory = new Int32Array(wasm.memory.buffer);
+    }
+    return cachegetInt32Memory;
+}
+
+function getArrayU8FromWasm(ptr, len) {
+    return getUint8Memory().subarray(ptr / 1, ptr / 1 + len);
+}
+/**
+* @param {Uint8Array} data
+* @param {number} level
+* @returns {Uint8Array}
+*/
+export function optimise(data, level) {
+    const retptr = 8;
+    const ret = wasm.optimise(retptr, passArray8ToWasm(data), WASM_VECTOR_LEN, level);
+    const memi32 = getInt32Memory();
+    const v0 = getArrayU8FromWasm(memi32[retptr / 4 + 0], memi32[retptr / 4 + 1]).slice();
+    wasm.__wbindgen_free(memi32[retptr / 4 + 0], memi32[retptr / 4 + 1] * 1);
+    return v0;
+}
+
+let cachedTextDecoder = new TextDecoder('utf-8');
+
+function getStringFromWasm(ptr, len) {
+    return cachedTextDecoder.decode(getUint8Memory().subarray(ptr, ptr + len));
+}
+
+export const __wbindgen_throw = function(arg0, arg1) {
+    throw new Error(getStringFromWasm(arg0, arg1));
+};
+