Changed the Requests/Response from tuples to named struct variants and also sorted in alphabetical order.
Replaced the ID generator functions from `globalscope` with a single function,
which returns a `RefMut` and can call the appropriate method to generate resource IDs.
Added WebIDL bindings for `GPUCommandEncoder`, `GPUCommandBuffer`, `GPUComputePassEncoder`, `GPUProgrammablePassEncoder`.
Implemented the `beginComputePass`, `copyBufferToBuffer` and `finish` functions of `GPUCommandEncoder`.
Implemented the `createCommandEncoder` function of `GPUDevice`.