Some dead code and duplicate data are cleaned up from the compiler.
Several parameters can be accessed directly from ShBuiltInResources
instead of creating a copy in TCompiler.

This also encapsulates some TCompiler member functions as private and
changes the remaining unprefixed TCompiler member variable names to
start with the m prefix.

BUG=angleproject:2068
TEST=angle_unittests

Change-Id: I6690aaf538b17e0f45460660272a21f82f1808a0
Reviewed-on: https://chromium-review.googlesource.com/c/1267503Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>