When producing an error from the uniformity analysis, add notes to
show the underlying reason for the uniformity requirement.
For function calls that are required-to-be-uniform, show the innermost
builtin call that has the requirement.
For function parameters that are required-to-be-uniform, recurse into
that function to show where its requirement comes from.
Add some new tests to specifically test the error messages.
Bug: tint:880
Change-Id: Ib166fdeceaffb156a3afc50ebc5a4ad0860dc002
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/89722
Reviewed-by: Ben Clayton <bclayton@google.com>
9c03abfb55