Implementation of GLSL to MSL translator

Bug: angleproject:2634
Change-Id: I66e2374b461548fac46163ea79790a488515e6b0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1887251
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>