Emitted when text is inserted into the widget by the user.
The default handler for this signal will normally be responsible for inserting the text, so by connecting to this signal and then stopping the signal with stop_emission, it is possible to modify the inserted text, or prevent it from being inserted entirely.
the new text to insert
the length of the new text, in bytes, or -1 if new_text is nul-terminated
the position, in characters, at which to insert the new text. this is an in-out parameter. After the signal emission is finished, it should point after the newly inserted text.