Wrap the texture expression in parentheses when it has lower
precendence than the function call operator.
Cast integer coordinates to unsigned integers as required by MSL.
Fixed: tint:536
Change-Id: I957e6be3c51044959e25e0be96c2d2c65db18187
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/53962
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
0f1efe04c3