Since HLSL doesn't support arrays as l-values, HLSL output needs to split
declarators that initialize arrays to variable declaration and assignment
implemented via a function call. To prepare for this, it is necessary that each
declarator has its own declaration.

BUG=angleproject:941
TEST=angle_end2end_tests, WebGL conformance tests

Change-Id: I43dee487578561c01dbde90c2f55a93dda2f057a
Reviewed-on: https://chromium-review.googlesource.com/266001Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>