The term "cancelling" is used with GCancellable, a user clicking a close
button is not that.
User input is usually described as "dismissing", so we use that term.
These are being replaced by GtkFontDialog
and GtkFontDialogButton
This commit only moves the headers for GtkFontChooserWidget and
GtkFontChooserDialog to deprecated/, and keeps the implementations
in gtk/, since they will eventually be salvaged into a private
GtkFontChooserWindow.