ES31: Support adjacency draw modes for geometry shader This patch implements adjacency primitive types as new draw modes on OpenGL back-ends. This patch also implements validations on the compatibilities among draw modes and geometry shader input primitive types. BUG=angleproject:1941 TEST=dEQP-GLES31.functional.geometry_shading.input.* dEQP-GLES31.functional.geometry_shading.negative.* Change-Id: I373ebfe88d7f50da3cc81adaf2d1b7f586b0932a Reviewed-on: https://chromium-review.googlesource.com/954715 Commit-Queue: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org>