BCursor: add a constructor with bitmap and point

* enhancement #15169
* get_mouse_bitmap(): also reads the colorspace from app_server.
* docs and tests

Change-Id: Iba63f8a2789530ae596c30b92f14828f31761d98
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3292
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

API Docs: various AppKit improvements

API docs: it's => its fix

Update App Kit Documentation.

The biggest change is the addition of \since to each method. I've gone
through old versions of the BeBook and documented what version of BeOS
each method was introduced in. I'm only counting production releases
so I'm starting with BeOS R3 ignoring all DR and PR releases. Likewise,
all methods new to Haiku are listed as being introduced \since Haiku R1
ignoring alpha releases.

Assign class docs for app and support to libbe group, not libroot

Move app and support class docs from libbe to libroot.

Also a few more style and spelling fixes.

Big docs cleanup.

* Fixed headers including:
- All rights reserved not All Rights Reserved.
- name, email@domain.com not name <email@domain.com>
- tabs and spaces
- Authors: not Documented by:
* Renamed string.dox to String.dox
* Renamed midixxx.dox files to MidiXxx.dox
* Moved images into images subdirectories and updated Doxfile.
* Re-format all files with tabs instead of spaces.
* Fix many spelling mistakes.
* Added all files, classes, structs, and enums to libbe group.

Add BCursor class documentation

Update App Kit Documentation.

The biggest change is the addition of \since to each method. I've gone
through old versions of the BeBook and documented what version of BeOS
each method was introduced in. I'm only counting production releases
so I'm starting with BeOS R3 ignoring all DR and PR releases. Likewise,
all methods new to Haiku are listed as being introduced \since Haiku R1
ignoring alpha releases.

Assign class docs for app and support to libbe group, not libroot

Move app and support class docs from libbe to libroot.

Also a few more style and spelling fixes.

Big docs cleanup.

* Fixed headers including:
- All rights reserved not All Rights Reserved.
- name, email@domain.com not name <email@domain.com>
- tabs and spaces
- Authors: not Documented by:
* Renamed string.dox to String.dox
* Renamed midixxx.dox files to MidiXxx.dox
* Moved images into images subdirectories and updated Doxfile.
* Re-format all files with tabs instead of spaces.
* Fix many spelling mistakes.
* Added all files, classes, structs, and enums to libbe group.

Add BCursor class documentation