Add optional access to ptr<>

This also completes the work to resolve the access controls for each
storage type.

Fixed: tint:846
Change-Id: Iab24057ec14620a2978ec63c4a91ba12d1bc6e9b
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/53381
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: James Price <jrprice@google.com>

test/bug/tint/221.wgsl

@@ -13,7 +13,7 @@ fn main() {
   var i : u32 = 0u;
   loop {
     if (i >= b.count) { break; }
-    let p : ptr<storage, u32> = &b.data[i];
+    let p : ptr<storage, u32, read_write> = &b.data[i];
     if ((i % 2u) == 0u) { continue; }
     *p = 0u;              // Set odd elements of the array to 0
     continuing {

test/bug/tint/492.wgsl

@@ -2,6 +2,6 @@
 [[group(0), binding(0)]] var<storage, read_write> buf : S;
 
 [[stage(compute)]] fn main() {
-  let p : ptr<storage, i32> = &buf.a;
+  let p : ptr<storage, i32, read_write> = &buf.a;
   *p = 12;
 }

test/bug/tint/744.wgsl.expected.spvasm

@@ -37,6 +37,7 @@
                OpMemberDecorate %Uniforms 0 Offset 0
                OpMemberDecorate %Uniforms 1 Offset 8
                OpMemberDecorate %Uniforms 2 Offset 16
+               OpDecorate %uniforms NonWritable
                OpDecorate %uniforms DescriptorSet 0
                OpDecorate %uniforms Binding 3
                OpDecorate %tint_symbol BuiltIn GlobalInvocationId

test/bug/tint/749.spvasm.expected.spvasm

@@ -49,6 +49,7 @@
                OpDecorate %gl_FragCoord BuiltIn FragCoord
                OpDecorate %buf0 Block
                OpMemberDecorate %buf0 0 Offset 0
+               OpDecorate %x_188 NonWritable
                OpDecorate %x_188 DescriptorSet 0
                OpDecorate %x_188 Binding 0
                OpDecorate %x_GLF_color Location 0