Add webgl/pending/conformance/context/context-attributes-alpha-depth-stencil-antialias.html from webgl/2.0.y
This makes it easier to add missing tests to the test suite when fixing a bug that is not covered by the test.
Created attachment 424228 [details]
Committed r275201: <https://commits.webkit.org/r275201>
All reviewed patches have been landed. Closing bug and clearing flags on attachment 424228 [details].