Rename our internal GActionMuxer, GActionObserver and GActionObservable
classes and interfaces to have names in our own namespace.
These classes were originally intended for GIO but turned out to be too
special-purpose to be useful there, so we never made them public API but
have just been copying them around (without bothering to properly rename
them). Now that other people will be copying them out of Gtk, it's even
more important to prevent this namespace abuse from spreading further.
First, ensure we always consume floating values, as documented.
Second (and more serious), don't try to query the action if the
action name is not set yet. This will cause crashes...
The current process of implementing GActionObserver is annoying and the
GSimpleActionObserver interface leaves a lot to be desired. Introduce a
new class, GtkActionHelper that gives you pretty much everything you'd
want to do as an implementor of GtkActionable.
The GtkActionHelper also features an "application" mode that is not
associated with a particular GtkWidget but rather with whatever widget
happens to be the active window of the given GtkApplication at a
particular point in time. This will be useful for the Mac OS menubar.
