Also fixes a bug where invalid stages may be specified for example if
AllGraphicsReadOnly or DepthStencilReadOnly layouts are used and
geometry or tessellation shaders are not supported by the
implementation.

Bug: angleproject:5557
Change-Id: Ia25a6aec8138c67701c63da65783263d8a7bda27
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2653911
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>