This patch adds the link validation on geometry shader varyings.

According to SPEC, geometry shader inputs should not be treated
as arrays for the purpose of interface matching.

This patch also moves the checks on fragment input bindings into
a single function.

BUG=angleproject:1941
TEST=angle_end2end_tests
     dEQP-GLES31.functional.shaders.linkage.es31.geometry.varying.*

Change-Id: Ib3ca64e28683e9688edc9432d43ff5a70c86117e
Reviewed-on: https://chromium-review.googlesource.com/929866Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>