writer/msl: Generate address spaces for pointers

Add more E2E tests to cover pointers with different storage classes.

Fixed: tint:815
Change-Id: I224a794cdf60648ce71dc9a0922d489542995be1
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/51404
Auto-Submit: James Price <jrprice@google.com>
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@chromium.org>

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

@@ -0,0 +1,6 @@
+[[stage(compute)]]
+fn main() {
+  var i : i32 = 123;
+  let p : ptr<function, i32> = &(i);
+  let use : i32 = (*(p) + 1);
+}