[spv-in] Rewrite the comparison image/sample handling.

Keep track of the comparison property per global variable instead of  type.
Only track images that can actually be comparison-sampled.
Instead of mutating the type, just add a new type in the end
if we detect it to be necessary, cloning the old name.

src/front/spv/error.rs

@@ -35,24 +35,22 @@ pub enum Error {
     InvalidVectorSize(spirv::Word),
     InvalidVariableClass(spirv::StorageClass),
     InvalidAccessType(spirv::Word),
-    InvalidAccess(Handle<crate::Expression>),
+    InvalidAccess(crate::Expression),
     InvalidAccessIndex(spirv::Word),
     InvalidBinding(spirv::Word),
-    InvalidImageExpression(Handle<crate::Expression>),
+    InvalidGlobalVar(crate::Expression),
     InvalidImageBaseType(Handle<crate::Type>),
     InvalidSampleImage(Handle<crate::Type>),
-    InvalidSamplerExpression(Handle<crate::Expression>),
     InvalidDepthReference(Handle<crate::Type>),
     InvalidAsType(Handle<crate::Type>),
-    InconsistentComparisonSampling(Handle<crate::Type>),
+    InconsistentComparisonSampling(Handle<crate::GlobalVariable>),
     WrongFunctionResultType(spirv::Word),
     WrongFunctionArgumentType(spirv::Word),
     MissingDecoration(spirv::Decoration),
     BadString,
     IncompleteData,
     InvalidTerminator,
     InvalidEdgeClassification,
-    UnexpectedComparisonType(Handle<crate::Type>),
     // incomplete implementation error
     UnsupportedRowMajorMatrix,
     UnsupportedMatrixStride(spirv::Word),