Remove some unnecessary TPublicType/TType conversions from the code, and
clean up code style. voidErrorCheck is changed to take TBasicType so that
it can be used with both TType and TPublicType.

TEST=angle_unittests
BUG=angleproject:941

Change-Id: I6f6cbc0761a4fc971299bad48864309009c54e7f
Reviewed-on: https://chromium-review.googlesource.com/264673Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>