Create a new GtkSourceCompletionContext for completion. The position at
which the completion using the new context will consider completion can
be provider by position. If position is NULL, the current cursor
position will be used.
a new GtkSourceCompletionContext. The reference being returned is a 'floating' reference, so if you invoke gtk_source_completion_show with this context you don't need to unref it.
Create a new GtkSourceCompletionContext for completion. The position at which the completion using the new context will consider completion can be provider by position. If position is NULL, the current cursor position will be used.