Improve Javadoc of predicates and functions

[codecholeric]

At the moment it is quite challenging to find a certain predicate or function, because users might need to know the domain model very well to find the necessary location (e.g. predicates like nameMatching(..) are defined within HasName.Predicates to be reused for everything that has a name, but at the same time users now need to know that JavaClass implements HasName to use these predicates).

While in the long term it might make sense to implement a better entry point API to improve discoverability, for now we can at least improve the documentation to link from more specific predicates to more generic ones. I.e. that I have some chance to discover

1. Javadoc on some method ...That(DescribedPredicate<? super JavaClass>) -> "you can find predefined predicates in JavaClass.Predicates
2. Javadoc on JavaClass.Predicates -> "due to inheritance you can find further applicable predicates in HasName.Predicates, HasModifiers.Predicates, ..."

[hankem]

Duly noted that many predefined predicates can be found within a subclass Predicates of the respective domain object or a common ancestor. 😂 SCNR

Wow, that was a lot of work, but it might probably help the users a lot!
(Let's hope that we'll keep this consistent in the future... 🙈)

I've just left some wording suggestions; they probably won't make much difference, just pick whatever you prefer.

[codecholeric]

Thanks so much for the extensive review!! 😄 I know that it is a lot of repetition and I also worry about keeping it consistent in the future. But I see no other choice, because you don't know from where users enter the API 🤷‍♂️ And the benefit of having this in many places IMHO outweighs if it should be inconsistent in some place in the future...