GtkSourceBuffer provides the ability to undo or redo the change to the note text-body. pluma uses gtksourceview 4, so we don't need to depend on two versions.
Merging this: it works, came from a trusted contributor, doesn't seem to be attracting any other reviewers, and reduces our dependency footprint for distros
GtkSourceBuffer provides the ability to undo or redo the change to the note text-body. pluma uses gtksourceview 4, so we don't need to depend on two versions.
fix #634