ES31: Add link validation on geometry shader itself This patch intends to support program link validation on geometry shader itself. A link error should occur when linking a program with a geometry shader that lacks input primitive or output primitive or the declaration of 'max_vertices'. This patch also adds the support of linking a program with geometry shader in angle_end2end_tests. BUG=angleproject:1941 TEST=angle_end2end_tests dEQP-GLES31.functional.shaders.linkage.es31.geometry.varying.rules.unspecified_* Change-Id: I25fb08514753102f5dd3ab86211c05d2ca4fd185 Reviewed-on: https://chromium-review.googlesource.com/898842 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>