GtkNotebook tabs DnD (but #73240)

[Carlos Garnacho <carlosg gnome org>]

Hi,

I've been lately working on adding drag and drop support in GtkNotebook
(both for reordering and detaching). The latest patches (attached in bug
#73240) implement the following API:

- gtk_notebook_[gs]et_tab_reorderable (): getter/setter for the
"reorderable" child property, used to mark an individual tab as
reorderable, it's turned off by default.

- gtk_notebook_[gs]et_tab_detachable (): ditto for the "detachable"
child property, uset to mark a tab as detachable, it's turned off by
default.

- gtk_notebook_[gs]et_group_id (): gets/sets a group ID for a notebook,
it's used to know whether 2 notebooks can exchange tabs through DnD, -1
(the default) means "no group", so detaching to other notebooks is not
allowed.

- gtk_notebook_set_window_creation_hook (): sets a global
GtkNotebookWindowCreationFunc, used when the dragged tab is dropped in
the root window, it should create a new window containing a notebook
where the tab will be attached, the window creation function may return
NULL to cancel the detaching. There's no default window creation
function, so dropping to root window won't be allowed by default.

- "tab-reordered", "tab-detached", "tab-attached" signals: emitted
respectively when a tab is reordered, detached from a notebook and
attached to a notebook.

Any comment about this API addition will be welcome :)

        Carlos