Make WebGPU resource creation async and prevent panic during shutdown if WebGPU is enabled.
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1. Make WebGPU resource creation async.
2. Remove some unused code in `WebGPURequest::RequestAdapter`.
3. Prevent panic during shutdown. Since WGPU thread is killed before script, sender and receiver in the script panic at either of the two places-
a. If a buffer is still alive, script tries to send `WebGPURequest::DestroyBuffer` to server while dropping the buffer during shutdown.
7170a69695/components/script/dom/gpubuffer.rs (L118-L122)7170a69695/components/script/dom/gpubuffer.rs (L182-L186)
b. Receiver in script-thread panics with `RecvError` as soon as sender on server side is dropped. 7170a69695/components/script/script_thread.rs (L1456-L1457)
r?@kvark
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- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#25472 (GitHub issue number if applicable)
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- [ ] There are tests for these changes OR
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07eb9ab3fe