TabbedPane drag and drop tabs reordering support.

[AndreiKud]

Fixes #1212

Same as in #1225 I used an open-source Java Swing components repo as a reference. Specifically DnDTabbedPane component.

Key notes:

1. Though the original component is heavily modified to fit in Jadx codebase, there are some untouched parts still, so I placed MIT license (added you as copyrighter) at the beginning of every DnD-related file. However, it will override your Apache 2.0 license for these specific files, are you ok with it? I also found other DnDTabbedPane implementations that used the original repo as a source, but didn't bother to license the code.
2. There are multiple modes for rendering "ghost" tab that we are dragging as described in TabDndGhostType.java. I haven't added UI settings for it, since it is the only one (well, mayby the ghost color as well) modifiable property of tabs behaviour and the setting will look wierdly empty. I suggest adding it with next configurable tabs feature.
3. Moved all tabs-related classes to separate package.
4. Tried to supply vague logic with commentaries.
5. Made an PR to original repo along the way: DnDTabbedPane. Idx for insertion selection fix. aterai/java-swing-tips#24.

[skylot]

@AndreiKud looks great! Thank you 👍

it will override your Apache 2.0 license for these specific files, are you ok with it?

I think it is fine as soon as it explicitly stated and MIT is more permissive

There are multiple modes for rendering "ghost" tab

Yeah, setting for this will be nice, because for me this ghost tab is not needed at all, only insertion mark is fine.

Made an PR to original repo along the way

Well done! 🙂