Create a new #GtkSourceCompletionContext for completion. The position where
the completion occurs can be specified 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 gtksource.completion.Completion.start with this context
you don't need to unref it.
Create a new #GtkSourceCompletionContext for completion. The position where the completion occurs can be specified by position. If position is null, the current cursor position will be used.