[mlir][sparse] Extend readCOOIndices to support overhead types beyond index_type.

[bixia]

Summary

This is to prepare for implementing the C API for reading a COO tensor to the
given buffers for indices and values.

[bixia]

Apply clang-format.

[wrengr]

mlir/include/mlir/ExecutionEngine/SparseTensor/File.h

269

Please rename rank to dimRank and rename r to d. (To make things forward compatible with the new terminology/style of D143800 and https://github.com/openxla/stablehlo/pull/1143)

[bixia]

Rename variables, rank => dimRank, r => d.

mlir/include/mlir/ExecutionEngine/SparseTensor/File.h

private:
 
   /// Reads the next line of the input file and parses the coordinates
   /// into the `indices` argument.  Returns the position in the `line`
   /// buffer where the element's value should be parsed from.  This method
   /// has been factored out from `readCOOElement` to minimize code bloat
   /// for the generated library.
   ///
   /// Precondition: `indices` is valid for `getRank()`.
-  char *readCOOIndices(uint64_t *indices);
+  template <typename I>
+  char *readCOOIndices(I *indices) {
+    readLine();
+    // Local variable for tracking the parser's position in the `line` buffer.
+    char *linePtr = line;
+    for (uint64_t dimRank = getRank(), d = 0; d < dimRank; ++d) {
+      // Parse the 1-based index.
+      uint64_t idx = strtoul(linePtr, &linePtr, 10);
+      // Store the 0-based index.
+      indices[d] = static_cast<I>(idx - 1);
+    }
+    return linePtr;
+  }
 
   /// The internal implementation of `readCOO`.  We template over
   /// `IsPattern` and `IsSymmetric` in order to perform LICM without
   /// needing to duplicate the source code.
   //
   // TODO: We currently take the `dim2lvl` argument as a `PermutationRef`
   // since that's what `readCOO` creates.  Once we update `readCOO` to
   // functionalize the mapping, then this helper will just take that

mlir/lib/ExecutionEngine/SparseTensor/File.cpp

 }
 
 /// Attempts to read a line from the file.
 void SparseTensorReader::readLine() {
   if (!fgets(line, kColWidth, file))
     MLIR_SPARSETENSOR_FATAL("Cannot read next line of %s\n", filename);
 }
 
-char *SparseTensorReader::readCOOIndices(uint64_t *indices) {
-  readLine();
-  // Local variable for tracking the parser's position in the `line` buffer.
-  char *linePtr = line;
-  for (uint64_t rank = getRank(), r = 0; r < rank; ++r) {
-    // Parse the 1-based index.
-    uint64_t idx = strtoul(linePtr, &linePtr, 10);
-    // Store the 0-based index.
-    indices[r] = idx - 1;
-  }
-  return linePtr;
-}
-
 /// Reads and parses the file's header.
 void SparseTensorReader::readHeader() {
   assert(file && "Attempt to readHeader() before openFile()");
   if (strstr(filename, ".mtx"))
     readMMEHeader();
   else if (strstr(filename, ".tns"))
     readExtFROSTTHeader();
   else