renamed SkSL types in preparation for killing precision modifiers

Bug: skia:
Change-Id: Iff0289e25355a89cdc289a0892ed755dd1b1c900
Reviewed-on: https://skia-review.googlesource.com/27703
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
117 files changed