[onnx][importer] Merge character sanitization into regex (llvm#3914)

Refactors llvm#3901 by merging
illegal character sanitization into the regex and removing call to
`replace()`.

python/torch_mlir/extras/onnx_importer.py

@@ -740,13 +740,9 @@ def _sanitize_name(self, name):
         if not name.isidentifier():
             name = "_" + name
 
-        # The presence of '-' characters in the initializer names can cause
-        # unintended side-effects when the IR is parsed during compilation.
-        # Simply replace all the occurrences of '-' in the name string when the
-        # dense resource is created.
-        name = name.replace("-", "_")
-
-        return re.sub("[:/]", "_", name)
+        # Remove characters that are invalid in MLIR identifier names.
+        # https://mlir.llvm.org/docs/LangRef/#identifiers-and-keywords
+        return re.sub("[:/-]", "_", name)
 
     def tensor_proto_to_attr(self, tp: onnx.TensorProto) -> Attribute:
         tensor_type = self.tensor_proto_to_builtin_type(tp)