AppKit: BMessage Add/Find/Get/Has/ReplaceNodeRef

This allows you to pass node_ref's around like you can entry_ref's.

Added node_ref_flatten(), node_ref_unflatten() and node_ref_swap() to
MessageUtils. These are close cousins to entry_ref_flatten(),
entry_ref_unflatten(), and entry_ref_swap() but for node_ref's.

Added B_NODE_REF_TYPE to TypeConstants.h in the Support Kit.

Added B_NODE_REF_TYPE to Debugger and ByteOrder in Support Kit,
B_NODE_REF_TYPE is treated the same as a B_REF_TYPE (entry_ref).

Add documentation for new NodeRef methods and B_NODE_REF_TYPE.

Change-Id: I32c6ed276bf1a7894a835b9fc9de5a882c35883c
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3182
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

Debugger: Call the GCC2 get_next_argument directly.

This codepath is only hit when we are using the GCC2 demangler,
so we should not use get_next_argument which tries to autodetect
what kind of symbol this is.

Debugger: Split into core library and application.

- Add subfolder src/kits/debugger which contains the debugger's core
functionality and lower layers. Correspondingly add headers/private/debugger
for shared headers to be used by clients such as the Debugger application
and eventual remote_debug_server. Adjust various files to account for
differences as a result of the split and moves.
- Add libdebugger.so to minimal Jamfile.