Initial implementation of GPUCommandEncoder
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Added WebIDL bindings for `GPUCommandEncoder`, `GPUCommandBuffer`, `GPUComputePassEncoder` and `GPUProgrammablePassEncoder`.
Implemented the `beginComputePass`, `copyBufferToBuffer` and `finish` functions of `GPUCommandEncoder`.
Implemented the `createCommandEncoder` function of `GPUDevice`.
This pull request is based on: #25700
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes addresses a part of #24706
cc @kvark @jdm @zakorgy
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0790c856d5