Auto merge of #27329 - kunalmohan:gpu-label, r=kvark

Update GPUObjectBase webidl and cleanup valid flags

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Update labels to be `USVString`
Remove `valid` flags in WebGPU resources. The only place where we still have that is `GPUCommandEncoder` (Only to validate the GPUCommandEncoder state. Not sure how errors would be handled/reported by server for copy commands).

r?@kvark

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