Implements:
- WebAssembly object,
- WebAssembly.Module constructor,
- WebAssembly.Instance constructor,
- WebAssembly.compile async method,
- and Module and Instance instance objects.

Also, changes ErrorThrower to support capturing errors in a promise reject.

Since we cannot yet compile without fixing the Wasm memory, and cannot validate a module without compiling, the Module constructor and compile method don't do anything yet but checking that their argument is a suitable BufferSource. Instead of a compiled module, the hidden state of a Module object currently is just that buffer.

BUG=

Review-Url: https://codereview.chromium.org/2084573002
Cr-Commit-Position: refs/heads/master@{#37143}