Vulkan: Add OES_shader_multisample_interpolation extension Addition of 'sample' qualifier keyword and 'interplateAt*' fragment shader builtin functions with autogen Bug: angleproject:3589 Change-Id: If358eb371fbcefffa715c8da4ba5e96eefaf6f52 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2477904 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>