ESSL 3.00 allows a wider variety of types of input/output variables
than ESSL 1.00, but there are still specific restrictions on structs,
matrices and arrays.

Some of the checks need to be implemented twice: once for array syntax
where the brackets are after the type, and another time for array syntax
where the brackets are after the variable name.

This requires fixes to constant folding unit tests which were previously
incorrectly using matrix outputs in fragment shaders.

New unit tests are added for several of the rules introduced, but some
cases are also covered by dEQP.

TEST=angle_unittests, dEQP-GLES.functional.shaders.linkage.varying.rules.*
BUG=angleproject:1061

Change-Id: I655b054cfe56d376db775b96a2bb41b3ac5740b0
Reviewed-on: https://chromium-review.googlesource.com/285482Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>