HaikuDepot TextView: add support for hyperlinks/clikable areas

Specific text spans can be assigned a cursor and BMessage to send when
they are clicked. This allows for implementing hyperlinks, specific
popup menus, and clickable text of any type.

With some extra work it can also be used to implement spell checking
suggestions, buttons, and so on.

Change-Id: I390e0c44656da76a950c432bdd934bd51af49baf
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7130
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

HaikuDepot: Remove Custom List

Closes #15534

Change-Id: I23fa60145607c3e8f25552f24c5e2c630b940537
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3758
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

TextDocument: Change _Insert() to use TextDocument

In preparation for implementing Undo/Redo support, we need _Insert() to
take a TextDocument instead of a BString, CharacterStyle and ParagraphStyle.
When a chunk of the TextDocument has been removed, we need to be able to
Insert() that as part of the Undo operation. Not well tested, but typing
still works.

Text frame work: Implement sending TextChangedEvents

TextDocument:
* Moved implementation of Remove() and Insert() into private methods.
* Reimplement all public Insert() methods and Remove() on top of Replace().
* In Replace(), send a TextChangedEvent. Added TODO for sending a
TextChangingEvent, although at this point, I am not sure if it will be
needed at all.

HaikuDepot: Added UndoableEditListener list to TextDocument

This is all work in progress. The plan is to move the code that does any
actual changes to the TextDocument into UndoableEdit implementations, then
emit these edits to interesed listeners. They can then store them to
implement the edit history. If there are not listeners, the edits will
simply be released after they've done their work.
Implemented so far is only the support for storing the edit listeners.

Renamed HaikuDepot's home to haikudepot.

* This closes #10699. I mentioned that to stippi after his first commit
of HaikuDepot, anyway :-)

TextDocument: Change _Insert() to use TextDocument

In preparation for implementing Undo/Redo support, we need _Insert() to
take a TextDocument instead of a BString, CharacterStyle and ParagraphStyle.
When a chunk of the TextDocument has been removed, we need to be able to
Insert() that as part of the Undo operation. Not well tested, but typing
still works.

Text frame work: Implement sending TextChangedEvents

TextDocument:
* Moved implementation of Remove() and Insert() into private methods.
* Reimplement all public Insert() methods and Remove() on top of Replace().
* In Replace(), send a TextChangedEvent. Added TODO for sending a
TextChangingEvent, although at this point, I am not sure if it will be
needed at all.

HaikuDepot: Added UndoableEditListener list to TextDocument

This is all work in progress. The plan is to move the code that does any
actual changes to the TextDocument into UndoableEdit implementations, then
emit these edits to interesed listeners. They can then store them to
implement the edit history. If there are not listeners, the edits will
simply be released after they've done their work.
Implemented so far is only the support for storing the edit listeners.

Renamed HaikuDepot's home to haikudepot.

* This closes #10699. I mentioned that to stippi after his first commit
of HaikuDepot, anyway :-)