* re-land after mac compilation fix (unsupported c++11 initializer) *

This change adds constant folding support for following geometric
built-ins:
    - length, distance, dot, cross, normalize, faceforward,
      reflect and refract.

BUG=angleproject:913
TEST=angle_unittests, dEQP Tests
dEQP-GLES3.functional.shaders.constant_expressions.builtin_functions.geometric.*
(56 tests started passing with this change)

Change-Id: I236fc0c1af47a63f359564500c711e6bedf1c808
Reviewed-on: https://chromium-review.googlesource.com/274789Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>