[Builder] Search and replace - reusable frontend

[Sébastien Wilmet <swilmet gnome org>]

Hi,

The mockups for a new search and replace UI are really nice:
https://wiki.gnome.org/Apps/Builder/SearchAndReplace

Builder is not the only application that would benefit from the new UI.
Any text editor or IDE needs such feature, so it would be nice to make
the implementation reusable. I.e. depend only on GTK+, possibly the
libgd, and GtkSourceView.

Maybe even decouple the frontend from the controller, so that only the
controller depends on GtkSourceView (supposing that the GtkSourceSearch*
API will be used).

And a search and replace UI makes total sense to include it in
GtkSourceView. (but maybe not directly, in case refactorings are needed
and the API needs to change).

Best regards,
Sébastien