Honor lowp/mediump/highp precision qualifiers in DSLParser.

(Added bsalomon@ for public API review)

Change-Id: Id0e7f656d68f2c7bec2c38ca7ccc8c6bb49e7e91
Bug: skia:12248
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/436570
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
5 files changed