[WebGPU] Use dlsym() to implement wgpuGetProcAddress()
<rdar://problem/104543828>
Pull request: https://github.com/WebKit/WebKit/pull/8965
Committed 259264@main (7ce9becab5ac): <https://commits.webkit.org/259264@main> Reviewed commits have been landed. Closing PR #8965 and removing active labels.