Output the array brackets and the array size correctly when a function's
return value type is array.

Tested with WebGL 2 test sdk/tests/deqp/data/gles3/shaders/arrays.html

BUG=angleproject:971
TEST=WebGL 2 conformance tests

Change-Id: I63aa8c54d2696f65351b23acb0749a487298ddfb
Reviewed-on: https://chromium-review.googlesource.com/265410Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>