Fix negated ".not" modifier usage edge case

[santino]

Hey @MicheleBertoli,
quick PR to fix a small edge case introduced in #206.

This is to fix a scenario which would cause the following test to fail when it shouldn't

  const Button = styled.button`
    opacity: .65;
  `

  expect(<Button />).not.toHaveStyleRule('opacity', undefined)

Info

Since the opacity rule is applied to Button we can also write a test to check that the rule should not be undefined.
I consider this an edge case since this test is certainly convoluted and possibly pointless as most likely if you have a rule applied you want to write a test to check its value.

Fix

When the requested rule is undefined and the expected value is not passed or falsy and the negated .not modifier is used then we can return directly false to make our test pass without any need to use the matcherTest util which would always return true, since it evaluates expect(undefined).toEqual(undefined).
If the above conditions don't apply then we leave the matching logic to the matcherTest util as before.

This approach avoid the invocation of a function when is not required (as the result is predictable) and also simplifies the logic as it doesn't require flipping of the assertion.

Notes

• More comprehensive tests have been added on the use of the negated .not modifier with and without values.
• As usual the changes are applied to both web and native.
• I took the opportunity of this additional PR to also fix the types, since now as part of toHaveStyleRule to work with not passed expected value and negated ".not" modifier #206 the expected value is actually optional.

I actually realised this was probably going to create the issue mentioned above the day after opening #206 but have had a very crazy week and didn't manage to push a fix earlier.
Now that is weekend I finally got 5mins to get this sorted; sorry it will require you to publish v6.3.1 🙏

[MicheleBertoli]

Thank you very much, @santino.
I would also consider .not undefined an edge case, but I appreciate you enabled the ability to use it.
As usual, awesome PR 🙌