elementary textpath: support legacy APIs

elementary textpath: support legacy APIs

Summary:
Efl.Ui.Textpath was added when we were developing new interfaces.
So, basically, it does not support 'legacy' APIs. ex) elm_textpath_add
But, in Tizen, the legacy APIs had been delivered in old version of EFL.
To reduce maintainning cost between the platforms, this patch will be helpful.
@feature

Test Plan: N/A

Reviewers: Hermet, woohyun, zmike, cedric, herdsman

Reviewed By: Hermet

Subscribers: #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D7033