added SPIR-V RelaxedPrecision

Bug: skia:5524
Change-Id: I716b6bb8da95acb72ba71d083eb8b40cafbc6af8
Reviewed-on: https://skia-review.googlesource.com/19266
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
2 files changed