Auto merge of #24250 - imiklos:webglsync, r=jdm

Initial implementation of WebGLSync

This patch adds initial support for [WebGLSync](https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.14).

Note:
There is no test for the isSync, deleteSync and waitSync functions in the `conformance2/sync/sync-webgl-specific.html`.

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