Proposed Cleanup items for BeanPropertyIntrospector

[Shounaks]

A small effort to reduce complexity.

P.S. sorry for formatting, 😂

Reasoning:
BeanPropertyIntrospector is the brain of this library, and it does too much with too little documentation :

1. It does not save the state,
2. It has only 2 methods getting used, while other are helper methods, so only those 2 should be exposed as static
3. this class is self sufficient. i.e. it does not rely on other class or has to generate new object every time it will get used.

Pending Items

• test cases passed
• adding javadocs for methods

[cowtowncoder]

This will need to wait past 2.17 release, considered for 2.18.

But one quick note: if changing functionality to static methods, sub-classing no longer possible.
I think that I may have intended this to be a possible extension point, so developers could replace it with a sub-class implementation with suitable overrides.
If so, I wouldn't want to change it from regular class into containers of static methods.

[cowtowncoder]

Ah. Actually... ok, no. I was wrong: there is no way to override it, regardless of my original thinking. Annotation-support package actually has AnnotationBasedIntrospector which ideally should be sub-class, I think.

So there is room for re-considering what to do here. After 2.17.0 release :)

[Shounaks]

Can be optimized a bit more, and JavaDocs are remaining.

[pjfanning]

probably can't make a class final in a patch - needs a minor release ideally

[pjfanning]

can't change a public method to be static in a patch

[Shounaks]

I get your concern, this change can have unforeseen side-effects.
Currently this is just a proof of concept, to simplify and cleanup this class.

we can take items from here individually (if not all). or not use this at all (whatever is feasible)

[Shounaks]

I gave it a bit of thought, I believe the documentation is good enough, so not changing anymore.