Detect unintended comma at the end of expression

I would be great to have a rule that will detect cases such this:

instance = MyClass(arg1, arg2),

As it is most likely a typo. If someone wants a tuple, the preferred form would be (item,).

[ambv]

I’m only worried about the additional overhead for just this one check. lib2to3 is in Python so it’s going to slow down Bugbear a bit. We can do it and measure how bad that slowdown is but I have a feeling this is a better job for Black to always insert parentheses around single-element tuples to make this obvious.

[gaul]

Not to deter adding this to bugbear, but flake8_tuple finds unintended tuples.