The patch adds functionality to determine whether compiler output belongs
to the ESSL, GLSL, HLSL or Vulkan output family. The new functions can
be now used in other parts of the compiler in which code paths are
selected based on the compiler output.

BUG=angleproject:2062
TEST=angle_unittests

Change-Id: I45ccf63f0a756c60df47a679c2da9f60856d5918
Reviewed-on: https://chromium-review.googlesource.com/558990Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>