This patch intends to implement Geometry Shader inputs and
outputs in ANGLE GLSL compiler.

1. Only accept arrays as the inputs of a Geometry Shader.
2. Allow unsized arrays as the inputs of a Geometry Shader after a
   valid input primitive declaration and assign size to them.
3. Implement Geometry Shader outputs.
4. Allow Geometry Shader inputs and outputs using interpolation
   qualifiers ('flat', 'smooth', 'centroid').
5. Allow using 'location' layout qualifier on Geometry Shader inputs
   and outputs.

BUG=angleproject:1941
TEST=angle_unittests

Change-Id: Ia7e250277c61f45c8479437b567c2831ff26b433
Reviewed-on: https://chromium-review.googlesource.com/650211
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>