tests: shortcuts like "Lt" should give same as "<"

In Issue #7775, @asmeurer said that `< and Lt should be the same`.  Here are some tests for that (which currently fail).
There's nothing that can be done about this, unfortunately.  [Explanation here](https://github.com/sympy/sympy/blob/master/sympy/core/relational.py#L466-L476); it does happen consistently, but it's by Python's rules, not SymPy's.  So it's futile to test for it.