This CL adds the initial generation of a loop construct into the
spirv-writer. This does not support break or continue yet.
Bug: tint:5
Change-Id: I41f5d9b634a1a4120f880c4143feacc7e58e2147
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/19620
Reviewed-by: David Neto <dneto@google.com>
dan sinclair