[onnx] Fix importer variable names to make `mlir` legal (#2690)

Some names for `onnx` identifiers are not legal in `mlir-ir`. Sanitize
so that the generated `ir` is legal.

python/torch_mlir/extras/onnx_importer.py

@@ -38,6 +38,7 @@ from typing import Optional
 from dataclasses import dataclass
 
 import numpy as np
+import re
 
 from ..ir import (
     ArrayAttr,
@@ -464,13 +465,18 @@ class ContextCache:
             # See TypeProto: sequence_type, map_type, optional_type, sparse_tensor_type.
             raise OnnxImportError(f"Unsupported ONNX TypeProto: {tp}")
 
+    def _sanitize_name(self, name):
+        if not name.isidentifier():  
+            name = "_" + name  
+        return re.sub("[:/]", "_", name)  
+
     def tensor_proto_to_attr(self, tp: onnx.TensorProto) -> Attribute:
         tensor_type = self.tensor_proto_to_builtin_type(tp)
         if tp.HasField("raw_data"):
             # Conveniently, DenseResourceElementsAttr shares the raw data
             # format. We just give it maximum numeric alignment.
             return DenseResourceElementsAttr.get_from_buffer(
-                tp.raw_data, tp.name, tensor_type, alignment=8
+                tp.raw_data, self._sanitize_name(tp.name), tensor_type, alignment=8
             )
         else:
             # We have to do a data type specific instantiation from proto fields.