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.
Implemented the `mapReadAsync` and fixed the `unmap` functions of `GPUBuffer`.
Added `mapped` internal slot for tracking the ArrayBuffer/Promise.
Added more states to the `GPUBufferState` enum.
Added WebIDL bindings for GPUBuffer, GPUBufferDescriptor, GPUBufferUsage
Implemented the `createBuffer` and `createBufferMapped` functions of GPUDevice