Add invoke operator function extensions for Function types

[Emirlol]

Just a little syntax sugar so we don't have to juggle between apply, get, get<primitive>, test, or accept. If it's invokeable, invoke it.

Hope you don't mind the PR.

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Some notes:

I had to update kotlin version to use Enum.entries, but then noticed there are already forEach style functions for the fast util types. If it's unnecessary, I can revert it back. Same goes for gradle version (well, what I said earlier applies mostly to the gradle version as kotlin-dsl uses the embedded kotlin version within gradle, but I had already updated kotlin by the time I figured this out).

Also, I'm not sure what to do for formatting. I might've accidentally reformatted some spaces into tabs. I see there's something called spotless, but I don't know how to use it and I didn't see a gradle task for it either.

[Emirlol]

It also dawned on me too late that the get style methods are called that since maps are literally implementations of them. While I don't get why a Map inherits a Function (it doesn't in the java stdlib) these methods also allow calling the map.

I don't think this is that bad by itself since it feels like the indexing operator, but the original get methods are also usable with the indexing operator. This means both of map(key) and map[key] do the same thing. The key point is that map[key] does not generalize to generic keys, since those are deprecated and the javadoc refers you to the specific method that returns the unboxed value. With invoke, those also work.
So, while not harmful, I don't know if this would be confusing or not.

[MukjepScarlet]

Don't use \t as indent

[MukjepScarlet]

I don't think this is that bad by itself since it feels like the indexing operator, but the original get methods are also usable with the indexing operator. This means both of map(key) and map[key] do the same thing. The key point is that map[key] does not generalize to generic keys, since those are deprecated and the javadoc refers you to the specific method that returns the unboxed value. With invoke, those also work.

This is interesting. get{ValueType} also exists in {Type}Lists.