wgsl: Implement invariant attribute

Make sure the other backends ICE on unrecognized attributes.

Add E2E tests, currently skipped for the other backends.

Bug: tint:772
Change-Id: I4e68d111ff79b19ebb6c574058a91debcb746011
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/57642
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

test/shader_io/invariant.wgsl

@@ -0,0 +1,4 @@
+[[stage(vertex)]]
+fn main() -> [[builtin(position), invariant]] vec4<f32> {
+  return vec4<f32>();
+}

test/shader_io/invariant.wgsl.expected.hlsl

@@ -0,0 +1,10 @@
+SKIP: FAILED
+
+../../src/writer/hlsl/generator_impl.cc:3056 internal compiler error: unhandled struct member attribute: invariant
+********************************************************************
+*  The tint shader compiler has encountered an unexpected error.   *
+*                                                                  *
+*  Please help us fix this issue by submitting a bug report at     *
+*  crbug.com/tint with the source program that triggered the bug.  *
+********************************************************************
+

test/shader_io/invariant.wgsl.expected.msl

@@ -0,0 +1,10 @@
+SKIP: FAILED
+
+../../src/writer/msl/generator_impl.cc:1990 internal compiler error: unhandled struct member attribute: invariant
+********************************************************************
+*  The tint shader compiler has encountered an unexpected error.   *
+*                                                                  *
+*  Please help us fix this issue by submitting a bug report at     *
+*  crbug.com/tint with the source program that triggered the bug.  *
+********************************************************************
+

test/shader_io/invariant.wgsl.expected.spvasm

@@ -0,0 +1,9 @@
+SKIP: FAILED
+
+
+[[stage(vertex)]]
+fn main() -> [[builtin(position), invariant]] vec4<f32> {
+  return vec4<f32>();
+}
+
+Failed to generate: unknown decoration

test/shader_io/invariant.wgsl.expected.wgsl

@@ -0,0 +1,4 @@
+[[stage(vertex)]]
+fn main() -> [[builtin(position), invariant]] vec4<f32> {
+  return vec4<f32>();
+}

test/shader_io/invariant_struct_member.wgsl

@@ -0,0 +1,8 @@
+struct Out {
+  [[builtin(position), invariant]] pos : vec4<f32>;
+};
+
+[[stage(vertex)]]
+fn main() -> Out {
+  return Out();
+}

test/shader_io/invariant_struct_member.wgsl.expected.hlsl

@@ -0,0 +1,10 @@
+SKIP: FAILED
+
+../../src/writer/hlsl/generator_impl.cc:3056 internal compiler error: unhandled struct member attribute: invariant
+********************************************************************
+*  The tint shader compiler has encountered an unexpected error.   *
+*                                                                  *
+*  Please help us fix this issue by submitting a bug report at     *
+*  crbug.com/tint with the source program that triggered the bug.  *
+********************************************************************
+

test/shader_io/invariant_struct_member.wgsl.expected.msl

@@ -0,0 +1,10 @@
+SKIP: FAILED
+
+../../src/writer/msl/generator_impl.cc:1990 internal compiler error: unhandled struct member attribute: invariant
+********************************************************************
+*  The tint shader compiler has encountered an unexpected error.   *
+*                                                                  *
+*  Please help us fix this issue by submitting a bug report at     *
+*  crbug.com/tint with the source program that triggered the bug.  *
+********************************************************************
+

test/shader_io/invariant_struct_member.wgsl.expected.spvasm

@@ -0,0 +1,14 @@
+SKIP: FAILED
+
+
+struct Out {
+  [[builtin(position), invariant]]
+  pos : vec4<f32>;
+};
+
+[[stage(vertex)]]
+fn main() -> Out {
+  return Out();
+}
+
+Failed to generate: unknown decoration

test/shader_io/invariant_struct_member.wgsl.expected.wgsl

@@ -0,0 +1,9 @@
+struct Out {
+  [[builtin(position), invariant]]
+  pos : vec4<f32>;
+};
+
+[[stage(vertex)]]
+fn main() -> Out {
+  return Out();
+}