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>

test/ptr_ref/store/local/struct_field.spvasm.expected.spvasm

@@ -1,16 +1,17 @@
 ; SPIR-V
 ; Version: 1.3
 ; Generator: Google Tint Compiler; 0
-; Bound: 15
+; Bound: 18
 ; Schema: 0
                OpCapability Shader
                OpMemoryModel Logical GLSL450
                OpEntryPoint GLCompute %main "main"
                OpExecutionMode %main LocalSize 1 1 1
-               OpName %main "main"
+               OpName %main_1 "main_1"
                OpName %S "S"
                OpMemberName %S 0 "i"
                OpName %V "V"
+               OpName %main "main"
                OpMemberDecorate %S 0 Offset 0
        %void = OpTypeVoid
           %1 = OpTypeFunction %void
@@ -22,10 +23,15 @@
      %uint_0 = OpConstant %uint 0
 %_ptr_Function_int = OpTypePointer Function %int
       %int_5 = OpConstant %int 5
-       %main = OpFunction %void None %1
+     %main_1 = OpFunction %void None %1
           %4 = OpLabel
           %V = OpVariable %_ptr_Function_S Function %9
          %13 = OpAccessChain %_ptr_Function_int %V %uint_0
                OpStore %13 %int_5
                OpReturn
                OpFunctionEnd
+       %main = OpFunction %void None %1
+         %16 = OpLabel
+         %17 = OpFunctionCall %void %main_1
+               OpReturn
+               OpFunctionEnd