ES31: Support EXT_geometry_shader in GLSL compiler This patch intends to support "EXT_geometry_shader" as a valid extension string in ANGLE GLSL compiler. We decide to support it because in dEQP-GLES31 all geometry shader related tests are using "EXT_geometry_shader" instead of "OES_geometry_shader". 1. Support new extension string "EXT_geometry_shader" 2. Enable geometry shader layout qualifiers with EXT_geometry_shader 3. Enable geometry shader builtins with EXT_geometry_shader BUG=angleproject:1941 TEST=angle_unittests Change-Id: Iaedd01a9100ccf56243c957db36ff0c983d17060 Reviewed-on: https://chromium-review.googlesource.com/737933 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>