implemented the pipeline state builder for metal gpu backend

Bug: skia:
Change-Id: I9fc23de2e55ae3386aa8c0b8cdf540da63f19661
Reviewed-on: https://skia-review.googlesource.com/145156
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Timothy Liang <timliang@google.com>
6 files changed