[tint] Add RW storage textureLoad overloads

Adds them to the intrinsics table but no codegen support yet.

Bug: tint:2007

Change-Id: I4e3b768461ce06016e1ae6a4bf02ca70d0584237
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/145982
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
diff --git a/test/tint/builtins/gen/var/textureLoad/6e903f.wgsl.expected.msl b/test/tint/builtins/gen/var/textureLoad/6e903f.wgsl.expected.msl
new file mode 100644
index 0000000..2f3e8dc
--- /dev/null
+++ b/test/tint/builtins/gen/var/textureLoad/6e903f.wgsl.expected.msl
@@ -0,0 +1,35 @@
+SKIP: FAILED
+
+
+enable chromium_experimental_read_write_storage_texture;
+
+@group(1) @binding(0) var arg_0 : texture_storage_3d<rgba8sint, read_write>;
+
+fn textureLoad_6e903f() {
+  var arg_1 = vec3<i32>(1i);
+  var res : vec4<i32> = textureLoad(arg_0, arg_1);
+  prevent_dce = res;
+}
+
+@group(2) @binding(0) var<storage, read_write> prevent_dce : vec4<i32>;
+
+@vertex
+fn vertex_main() -> @builtin(position) vec4<f32> {
+  textureLoad_6e903f();
+  return vec4<f32>();
+}
+
+@fragment
+fn fragment_main() {
+  textureLoad_6e903f();
+}
+
+@compute @workgroup_size(1)
+fn compute_main() {
+  textureLoad_6e903f();
+}
+
+Failed to generate: builtins/gen/var/textureLoad/6e903f.wgsl:24:8 error: MSL backend does not support extension 'chromium_experimental_read_write_storage_texture'
+enable chromium_experimental_read_write_storage_texture;
+       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+