Implement mixed vector-scalar float % operator

W3C consensus on https://github.com/gpuweb/gpuweb/issues/2450
Spec change: https://github.com/gpuweb/gpuweb/pull/2495

Bug: tint:1370
Change-Id: I85bb9c802b0355bc53aa8dbacca8427fb7be1ff6
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/84880
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>

test/tint/expressions/binary/mod/vec3-scalar/u32.wgsl

@@ -0,0 +1,6 @@
+@stage(compute) @workgroup_size(1)
+fn f() {
+    let a = vec3<u32>(1u, 2u, 3u);
+    let b = 4u;
+    let r : vec3<u32> = a % b;
+}