Improve error message when constructing a Tensor with an invalid element type (NFC)

mlir/lib/IR/StandardTypes.cpp

 // TensorType
 //===----------------------------------------------------------------------===//
 
 // Check if "elementType" can be an element type of a tensor. Emit errors if
 // location is not nullptr.  Returns failure if check failed.
 static LogicalResult checkTensorElementType(Location location,
                                             Type elementType) {
   if (!TensorType::isValidElementType(elementType))
-    return emitError(location, "invalid tensor element type");
+    return emitError(location, "invalid tensor element type: ") << elementType;
   return success();
 }
 
 /// Return true if the specified element type is ok in a tensor.
 bool TensorType::isValidElementType(Type type) {
   // Note: Non standard/builtin types are allowed to exist within tensor
   // types. Dialects are expected to verify that tensor types have a valid
   // element type within that dialect.