[mlir][NFC] Mark type converter in populate... functions as const (#111250)

This commit marks the type converter in `populate...` functions as
`const`. This is useful for debugging.

Patterns already take a `const` type converter. However, some
`populate...` functions do not only add new patterns, but also add
additional type conversion rules. That makes it difficult to find the
place where a type conversion was added in the code base. With this
change, all `populate...` functions that only populate pattern now have
a `const` type converter. Programmers can then conclude from the
function signature that these functions do not register any new type
conversion rules.

Also some minor cleanups around the 1:N dialect conversion
infrastructure, which did not always pass the type converter as a
`const` object internally.

mlir/lib/Dialect/SparseTensor/Transforms/SparseTensorCodegen.cpp

@@ -746,8 +746,8 @@ class SparseTensorAllocConverter
     : public OpConversionPattern<bufferization::AllocTensorOp> {
 public:
   using OpConversionPattern::OpConversionPattern;
-  SparseTensorAllocConverter(TypeConverter &typeConverter, MLIRContext *context,
-                             bool enableInit)
+  SparseTensorAllocConverter(const TypeConverter &typeConverter,
+                             MLIRContext *context, bool enableInit)
       : OpConversionPattern(typeConverter, context),
         enableBufferInitialization(enableInit) {}
 
@@ -808,8 +808,8 @@ private:
 class SparseTensorEmptyConverter : public OpConversionPattern<tensor::EmptyOp> {
 public:
   using OpConversionPattern::OpConversionPattern;
-  SparseTensorEmptyConverter(TypeConverter &typeConverter, MLIRContext *context,
-                             bool enableInit)
+  SparseTensorEmptyConverter(const TypeConverter &typeConverter,
+                             MLIRContext *context, bool enableInit)
       : OpConversionPattern(typeConverter, context),
         enableBufferInitialization(enableInit) {}
 
@@ -850,7 +850,7 @@ class SparseTensorDeallocConverter
     : public OpConversionPattern<bufferization::DeallocTensorOp> {
 public:
   using OpConversionPattern::OpConversionPattern;
-  SparseTensorDeallocConverter(TypeConverter &typeConverter,
+  SparseTensorDeallocConverter(const TypeConverter &typeConverter,
                                MLIRContext *context, bool createDeallocs)
       : OpConversionPattern(typeConverter, context),
         createDeallocs(createDeallocs) {}
@@ -1411,7 +1411,7 @@ struct SparseAssembleOpConverter : public OpConversionPattern<AssembleOp> {
 struct SparseDisassembleOpConverter
     : public OpConversionPattern<DisassembleOp> {
   using OpConversionPattern::OpConversionPattern;
-  SparseDisassembleOpConverter(TypeConverter &typeConverter,
+  SparseDisassembleOpConverter(const TypeConverter &typeConverter,
                                MLIRContext *context)
       : OpConversionPattern(typeConverter, context) {}
 
@@ -1604,7 +1604,7 @@ struct SparseHasRuntimeLibraryConverter
 /// Populates the given patterns list with conversion rules required for
 /// the sparsification of linear algebra operations.
 void mlir::populateSparseTensorCodegenPatterns(
-    TypeConverter &typeConverter, RewritePatternSet &patterns,
+    const TypeConverter &typeConverter, RewritePatternSet &patterns,
     bool createSparseDeallocs, bool enableBufferInitialization) {
   patterns.add<
       SparseAssembleOpConverter, SparseDisassembleOpConverter,