Make a more complete type stub for `Tensor`

[shuttle1987]

Given that Tensor is a foundational piece we need to get good stubs for it. Currently there is only this:

tensorflow-stubs/tensorflow-stubs/__init__.pyi

Lines 81 to 82 in f000ae4

	class Tensor:
	pass

With no type stubs for __init__ or anything else. The coverage here needs to be improved.

[shuttle1987]

Tensor class is defined here: https://github.com/tensorflow/tensorflow/blob/0e53c66f338a60be5ea348fdeb7b19e5b579971f/tensorflow/python/framework/ops.py#L198