tint: Show the reason for a uniformity requirement

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>

test/tint/bug/tint/943.spvasm.expected.glsl

@@ -1,4 +1,5 @@
 warning: parameter 'dimInner' of 'mm_matMul_i1_i1_i1_' must be uniform
+note: 'workgroupBarrier' must only be called from uniform control flow
 #version 310 es
 
 struct Uniforms {

test/tint/bug/tint/943.spvasm.expected.hlsl

@@ -1,4 +1,5 @@
 warning: parameter 'dimInner' of 'mm_matMul_i1_i1_i1_' must be uniform
+note: 'workgroupBarrier' must only be called from uniform control flow
 static int dimAOuter_1 = 0;
 cbuffer cbuffer_x_48 : register(b3, space0) {
   uint4 x_48[5];

test/tint/bug/tint/943.spvasm.expected.msl

@@ -1,4 +1,5 @@
 warning: parameter 'dimInner' of 'mm_matMul_i1_i1_i1_' must be uniform
+note: 'workgroupBarrier' must only be called from uniform control flow
 #include <metal_stdlib>
 
 using namespace metal;

test/tint/bug/tint/943.spvasm.expected.spvasm

@@ -1,4 +1,5 @@
 warning: parameter 'dimInner' of 'mm_matMul_i1_i1_i1_' must be uniform
+note: 'workgroupBarrier' must only be called from uniform control flow
 ; SPIR-V
 ; Version: 1.3
 ; Generator: Google Tint Compiler; 0

test/tint/bug/tint/943.spvasm.expected.wgsl

@@ -1,4 +1,5 @@
 warning: parameter 'dimInner' of 'mm_matMul_i1_i1_i1_' must be uniform
+note: 'workgroupBarrier' must only be called from uniform control flow
 struct Uniforms {
   NAN : f32,
   @size(12)