This patch implements GL_REFERENCED_BY_GEOMETRY_SHADER as a valid
property of program interfaces.

BUG=angleproject:1941
TEST=angle_end2end_tests
     dEQP-GLES31.functional.geometry_shading.query.referenced_by_geometry_shader

Change-Id: Id9659313d371dbfc7d00bf9d816df4449fbf29ec
Reviewed-on: https://chromium-review.googlesource.com/1025281Reviewed-by: Jiajia Qin <jiajia.qin@intel.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>