Canvas text cursor: move to Efl.Canvas.Text namespace

Canvas text cursor: move to Efl.Canvas.Text namespace

Originally it was its own object.
There are some valid claims that there is no justification for it to
remain an object.
Furthermore, it's apparent that it added little benefit: changes of
each cursors, in practice, triggered a query for all objects of the
same textblock. There wasn't real advantage to have a finer resolution
of controlling the cursors with their own events.

This ports back a lot of code, and changes a lot of other code in the
higher-up widgets, such as Efl.Ui.Text and co.

The usage was replaces from:
  efl_canvas_text_cursor_char_next(cur_obj)
to
  efl_canvas_text_cursor_char_next(text_obj, cur_obj)
that is, it is an operations on the TEXT OBJECT, rather than on the
(now removed) cursor object.

So, one less efl object to worry about now.
Hopefully, the port went smooth.