Show what types of inputs are allowed

[justinchuby]

It would be helpful to show what types of inputs are allowed/expected types in eager mode calls, the name of the argument, as well as how one can make it right.

The current message is

Traceback (most recent call last):
  File "/home/justinchu/dev/onnx-script/playground/test_func.py", line 13, in <module>
    result = LeakyRelu(np.array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], dtype=np.float32), 0.1)
  File "/home/justinchu/dev/onnx-script/onnxscript/values.py", line 192, in __call__
    return self._usercall(*args, **kwargs)
  File "/home/justinchu/dev/onnx-script/onnxscript/values.py", line 203, in _usercall
    raise TypeError(f"Unexpected input type {type(a)} for an input {i}.")
TypeError: Unexpected input type <class 'float'> for an input 1.

https://github.com/microsoft/onnx-script/blob/de7b00a57894d5cbbfb8a739c5a49f80f73a34cd/onnxscript/values.py#L203