[WebGPU] Create and use WebGPUPtr in PAL/WebGPU/Impl
<rdar://problem/110198845>
Pull request: https://github.com/WebKit/WebKit/pull/14650
Committed 264884@main (979cf8ac3452): <https://commits.webkit.org/264884@main> Reviewed commits have been landed. Closing PR #14650 and removing active labels.