Debugger: add support for executable file refs

Adds support for handling executable files in the
Debugger::RefsReceived function.

This change
* makes Deskbar menu->Recent Applications->Debugger->A recently opened
executable open the executable instead of simply opening the
Teams window, and
* allows dragging and dropping an executable onto the application's
icon.

Change-Id: I8e70e7929188301ce976f1f14e885236d3cb2b0a
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6299
Reviewed-by: Rene Gollent <rene@gollent.com>
Tested-by: Automation <automation@haiku-os.org>

Usability improvements in StartTeamWindow

- Enlarge the window's width so a larger part of the path will fit in the TextBox.

- Apply the existing path to the BFilePanel before browsing. It improve
usability when you paste a path or type a new one in the TextBox
then click on the browse button to choose the application
or fine tune the directory.

Please not that it is a best effort feature : if the file or the directory does
not exist, the BFilePanel will fallback to the old behavior :
showing the previously selected file/directory in the session
(or home directory).

Change-Id: I504a1ec72f9f7a236e2e37039961fddc58218eae
Reviewed-on: https://review.haiku-os.org/672
Reviewed-by: Rene Gollent <rene@gollent.com>

Debugger: Cleanup.

- Split MessageCodes.h into a second file that separates out the
application-specific message codes from those used by the core.
Adjust includes accordingly. No functional change.

Debugger: StartTeamWindow Style fix.

Debugger: Rework to fully use TargetHostInterface.

Application objects:
- Rework and simplify to take into account that they will no longer be
directly managing the team debugger list. Requests to start a new debugger
are still funnelled through here however, and as such, said requests must
now provide the appropriate target host to start with. Adjust StartTeamWindow
and TeamsWindow accordingly.
- On global init, always create an instance of the local interface.

TargetHostInterface:
- Convert to BLooper and implement TeamDebugger's Listener interface.
TargetHostInterfaces now directly manage their TeamDebugger instances,
and consequently take over the equivalent duties that the main application
previously had.
- Adjust signatures of Attach/CreateTeam to add const. Adjust
LocalTargetHostInterface accordingly.
- Add accessor to determine if a given interface is local or not. Will be
needed for the TeamDebugger's file manager eventually so it knows if it
needs to request remote files if no matching local file is found.
- Add accessor to start a TeamDebugger instance, and corresponding options
structure.

TargetHostInterfaceRoster:
- Minor adjustments to host interface initialization to take into account
needing to start the looper.
- Add accessor for number of running team debuggers, for the main app to
use when deciding to quit.

TeamDebugger:
- Add accessor for SettingsManager. Needed for the case of a restart request,
as the host interfaces do not have direct access to it.

TeamsWindow:
- For now, always grab the local host interface when initializing the window.
Once the remote interface is implemented, this will need to be adjusted, but
the appropriate UI for creating/selecting it is needed first anyways.

With these changes, the main application is fully host-agnostic, and all
management of actual debuggers is delegated to their parent host interfaces.
There still needs to be a listener interface for the host interface and/or
roster though, so that the application can be made aware of when debuggers
quit, as this drives whether it's time to terminate the app or not.

Debugger: Cleanups.

General:
- Move all smaller prompt/edit windows to a dedicated subfolder.

Debugger/TeamsWindow/StartTeamWindow:
- Move management of StartTeamWindow to application, rather than
Teams window.

TeamWindow:
- Add top level menu item for commands that aren't specific to the
current team. This currently consists of requesting that the
Teams window be shown, and directly starting a new team.

Fixes part of #11659 (no way to start additional teams if Debugger was
initially started with a specific team).

Debugger: Cleanups.

General:
- Move all smaller prompt/edit windows to a dedicated subfolder.

Debugger/TeamsWindow/StartTeamWindow:
- Move management of StartTeamWindow to application, rather than
Teams window.

TeamWindow:
- Add top level menu item for commands that aren't specific to the
current team. This currently consists of requesting that the
Teams window be shown, and directly starting a new team.

Fixes part of #11659 (no way to start additional teams if Debugger was
initially started with a specific team).