Added validation to disallow usage of geometry shaders
without a vertex shader

Bug: angleproject:5579
Test: KHR-GLES32.core.geometry_shader.api.fs_gs_draw_call
Test: KHR-GLES32.core.geometry_shader.api.pipeline_program_without_active_vs
Change-Id: Ieeec544d514ac772416ab0427c1c1c5058276f98
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2796151Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>