wasm: use shared, imported memory

This switches our wasm build to use "shared" memory. Shared memory can
be shared across multiple web workers, which is something we'll want to
support for our multi-threaded behaviors later.

Shared memory has a number of different restrictions so this updates
zig-js to support it as well as updates some of our functions that need
to be aware of it.

example/app.ts

@@ -4,9 +4,11 @@ const zjs = new ZigJS();
 const importObject = {
   module: {},
   env: {
+    memory: new WebAssembly.Memory({ initial: 25, maximum: 65536, shared: true }),
     log: (ptr: number, len: number) => {
-      const view = new DataView(zjs.memory.buffer, ptr, Number(len));
-      const str = new TextDecoder('utf-8').decode(view);
+      const arr = new Uint8ClampedArray(zjs.memory.buffer, ptr, len);
+      const data = arr.slice();
+      const str = new TextDecoder('utf-8').decode(data);
       console.log(str);
     },
   },
@@ -20,8 +22,8 @@ fetch(url.href).then(response =>
 ).then(bytes =>
   WebAssembly.instantiate(bytes, importObject)
 ).then(results => {
+  const memory = importObject.env.memory;
   const {
-    memory,
     malloc,
     free,
     face_new,