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/store/local/i32.wgsl.expected.msl

@@ -3,7 +3,7 @@
 using namespace metal;
 kernel void tint_symbol() {
   int i = 123;
-  int* const p = &(i);
+  thread int* const p = &(i);
   *(p) = 123;
   *(p) = ((100 + 20) + 3);
   return;

test/ptr_ref/store/param/ptr.spvasm.expected.msl

@@ -1,7 +1,7 @@
 #include <metal_stdlib>
 
 using namespace metal;
-void func(int value, int* pointer) {
+void func(int value, thread int* pointer) {
   *(pointer) = value;
   return;
 }

test/ptr_ref/store/param/ptr.wgsl.expected.msl

@@ -1,7 +1,7 @@
 #include <metal_stdlib>
 
 using namespace metal;
-void func(int value, int* pointer) {
+void func(int value, thread int* pointer) {
   *(pointer) = value;
 }