Rename builtin(sample_mask_{in,out}) to builtin(sample_mask)

Removes the need to pass the storage class to the SPIR-V reader
builtin mapping function.

Added a deprecation warning for sample_mask_{in,out}.

Bug: tint:715
Change-Id: I948ff2de2d5de7bd05e1c6ff45bd721c856900e3
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/47743
Commit-Queue: James Price <jrprice@google.com>
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/inspector/inspector_test.cc

@@ -1041,7 +1041,7 @@ TEST_F(InspectorGetEntryPointTest, BuiltInsNotStageVariables) {
   auto* in_var1 = Param("in_var1", ty.u32(), {Location(0u)});
   Func("foo", {in_var0, in_var1}, ty.u32(), {Return(Expr("in_var1"))},
        {Stage(ast::PipelineStage::kFragment)},
-       {Builtin(ast::Builtin::kSampleMaskOut)});
+       {Builtin(ast::Builtin::kSampleMask)});
   Inspector& inspector = Build();
 
   auto result = inspector.GetEntryPoints();