Update: propEq to allow wider-typing for value in comparison

[Harris-Miller]

See this playground for full tests: https://tsplay.dev/mMlMdN

propEq needs a lot of updating. This MR is one of 3 towards that effort.

This first effort is just to update the typings to allow for a more correct range of typing when passing a val without yet knowing the type of obj

tl;dr is that when we know the type of val but not the type of obj, we're allowing for a wider type range for better support. These additions fix the following issues that the current typings don't support:

• val is string but the prob type is string | number
• prop type is | null (eg nullable)
• prop type is optional

The downside to these changes is that we lose errors when the types at obj.prop don't at all overlap with the type of val, but it will return never in those cases, which is better than nothing

Since the we know the type of val and obj at the same time with the full function signature propEq(val, name, obj), that signature can remain strict, since the above cases are not an issue with the full signature

TODO: update tests for allPass and anyPass so they don't rely on propEq. I don't want have to continuously update those as we update propEq. Those tests should stand on their own

[Nemo108]

This is a really great solution to the problem. It looks like it can fix almost all of the problems I face during development.

I agree about clearing up allPass and anyPass tests since they are unit tests and should not depend on any other function. However, it may be a better idea to make integrational tests somewhere, to ensure that functions can work okay together since sometimes typings updates can break the co-usage of the functions.