xwayland/glamor/gbm: use GBM_FORMAT_ARGB8888 for 24-bit depth on GL ES

Open Konstantin requested to merge rilian-la-te/xserver:xwayland-fix-black-windows-es into master

On some drivers (mesa included), when we request GBM_FORMAT_XRGB8888, driver set surface storage format to GL_RGB8, which breaks gles2 rendering. If we force set gbm_format to GBM_FORMAT_ARGB8888, then rendering will happen and working.

This is a screenshot of XWayland VirtualBox with !934 and MESA_GL_VERSION_OVERRIDE=2.0


Without !934, I will get black window instead of VirtualBox (#1356).

Fixes #1288 Fixes #1356

Request for review: @ofourdan @ajax @anholt

Edited by Konstantin

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