[WebGPU] Make weak getter methods return C++ references instead of strong Refs
<rdar://problem/104785462>
Pull request: https://github.com/WebKit/WebKit/pull/9286
Committed 259609@main (742f4888b2d3): <https://commits.webkit.org/259609@main> Reviewed commits have been landed. Closing PR #9286 and removing active labels.