Sync reserved token list to WGSL spec.

This CL updates the list of reserved words to match the WGSL spec. The
use of a reserved word is changed from an error to a deprecation at the
moment be cause the majority of the list would be new errors.

Bug: tint:1633 tint:1624
Change-Id: I498db41689cdd666dfb291b1a6761a1182c87ec8
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/98042
Reviewed-by: David Neto <dneto@google.com>
Reviewed-by: Ben Clayton <bclayton@chromium.org>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

test/tint/ptr_ref/load/local/ptr_function.wgsl

@@ -2,5 +2,5 @@
 fn main() {
   var i : i32 = 123;
   let p : ptr<function, i32> = &i;
-  let use : i32 = *p + 1;
+  let u : i32 = *p + 1;
 }