[mlir][sparse] minor code changes

[aartbik]

Summary

Submitting for Wren

[aartbik]

lint issue

mlir/include/mlir/Dialect/SparseTensor/IR/Enums.h

 enum class LevelFormat : uint8_t {
   Dense = 4,             // 0b0001_00
   Compressed = 8,        // 0b0010_00
   Singleton = 16,        // 0b0100_00
   CompressedWithHi = 32, // 0b1000_00
 };
 
 /// Returns string representation of the given dimension level type.
-inline std::string toMLIRString(DimLevelType dlt) {
+constexpr const char* toMLIRString(DimLevelType dlt) {
   switch (dlt) {
   // TODO: should probably raise an error instead of printing it...
   case DimLevelType::Undef:
     return "undef";
   case DimLevelType::Dense:
     return "dense";
   case DimLevelType::Compressed:
     return "compressed";

mlir/include/mlir/Dialect/SparseTensor/IR/SparseTensorAttrDefs.td

def SparseTensorDimSliceAttr : SparseTensor_Attr<"SparseTensorDimSlice", []> {
   let parameters = (
     ins
     "int64_t" : $offset,
     "int64_t" : $size,
     "int64_t" : $stride
   );
 
   let extraClassDeclaration = [{
+    void print(llvm::raw_ostream &os) const;
+
     /// Special value for dynamic offset/size/stride.
     static constexpr int64_t kDynamic = -1;
     static constexpr bool isDynamic(int64_t v) { return v == kDynamic; }
     static std::optional<uint64_t> getStatic(int64_t v);
     static std::string getStaticString(int64_t v);
 
     std::optional<uint64_t> getStaticOffset() const;
     std::optional<uint64_t> getStaticStride() const;

mlir/lib/Dialect/SparseTensor/IR/SparseTensorDialect.cpp

bool SparseTensorDimSliceAttr::isCompletelyDynamic() const {
   return isDynamic(getOffset()) && isDynamic(getStride()) &&
          isDynamic(getSize());
 }
 
 std::string SparseTensorDimSliceAttr::getStaticString(int64_t v) {
   return isDynamic(v) ? "?" : std::to_string(v);
 }
 
+void SparseTensorDimSliceAttr::print(llvm::raw_ostream &os) const {
+  os << '(';
+  os << getStaticString(getOffset());
+  os << ", ";
+  os << getStaticString(getSize());
+  os << ", ";
+  os << getStaticString(getStride());
+  os << ')';
+}
+
 void SparseTensorDimSliceAttr::print(AsmPrinter &printer) const {
-  printer << "(";
-  printer << getStaticString(getOffset());
-  printer << ", ";
-  printer << getStaticString(getSize());
-  printer << ", ";
-  printer << getStaticString(getStride());
-  printer << ")";
+  print(printer.getStream());
 }
 
 static ParseResult parseOptionalStaticSlice(int64_t &result,
                                             AsmParser &parser) {
   auto parseResult = parser.parseOptionalInteger(result);
   if (parseResult.has_value()) {
     if (parseResult.value().succeeded() && result < 0) {
       parser.emitError(