Deskbar: Save String object instead of pointer

And add a SetLabel() that sets the truncated label when the label gets set.

This will be useful so we can compare the truncated label to the normal label
to tell if the label is truncated or not.

Deskbar: Truncate menu item labels refactor

* Create a new TTruncatableMenuItem class to store the truncated string
and share the label truncation code between TTeamMenuItem and
TWindowMenuItem. In the future more shared code may be added to
this class, if so, the class name may change.
* The TTeamMenuItem and TWindowMenuItem classes inherit from
TTruncatableMenuItem, which inherits from BMenuItem.
* Make sure to truncate the label before drawing it in all cases.
* Some other related refactoring.

Fixes #9507

Deskbar: Save String object instead of pointer

And add a SetLabel() that sets the truncated label when the label gets set.

This will be useful so we can compare the truncated label to the normal label
to tell if the label is truncated or not.

Deskbar: Truncate menu item labels refactor

* Create a new TTruncatableMenuItem class to store the truncated string
and share the label truncation code between TTeamMenuItem and
TWindowMenuItem. In the future more shared code may be added to
this class, if so, the class name may change.
* The TTeamMenuItem and TWindowMenuItem classes inherit from
TTruncatableMenuItem, which inherits from BMenuItem.
* Make sure to truncate the label before drawing it in all cases.
* Some other related refactoring.

Fixes #9507