spirv-reader: switch to HLSL-style pipeline IO

- When storing to sample_mask output, write to the 0th element
- Only make a return struct if it has members
- Adjust type signedness coercion when loading special builtins.
- Adapt tests

- Update expectations for end-to-end tests

- Handle sample_mask with stride
  Input variables normally don't have layout. But they can have it
  up through SPIR-V 1.4.
  Handle this case in the SPIR-V reader, by seeing through the
  intermediate alias type created for the strided array type.

Bug: tint:508
Change-Id: I0f19dc1305d3f250dbbc0698a602288c34245274
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/54743
Auto-Submit: David Neto <dneto@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
diff --git a/test/ptr_ref/access/matrix.spvasm.expected.msl b/test/ptr_ref/access/matrix.spvasm.expected.msl
index beac5b5..355f903 100644
--- a/test/ptr_ref/access/matrix.spvasm.expected.msl
+++ b/test/ptr_ref/access/matrix.spvasm.expected.msl
@@ -1,10 +1,15 @@
 #include <metal_stdlib>
 
 using namespace metal;
-kernel void tint_symbol() {
+void main_1() {
   float3x3 m = float3x3(float3(0.0f, 0.0f, 0.0f), float3(0.0f, 0.0f, 0.0f), float3(0.0f, 0.0f, 0.0f));
   m = float3x3(float3(1.0f, 2.0f, 3.0f), float3(4.0f, 5.0f, 6.0f), float3(7.0f, 8.0f, 9.0f));
   m[1] = float3(5.0f, 5.0f, 5.0f);
   return;
 }
 
+kernel void tint_symbol() {
+  main_1();
+  return;
+}
+