elm_entry: use layout text/content aliases when text_set/get content_set/get/unset

elm_entry: use layout text/content aliases when text_set/get content_set/get/unset

Summary:
- elm_entry has elm.guide text part and it can be set by "guide".
- However when using text_aliases_get, this cannot be found.
- Add elm_obj_elm_layout_part_aliasing_eval() internal APIs to make entry
  use proper aliases.

Test Plan:
1. Run elementary test
           2. Observe search entry has guide text with "guide" part.
           3. Run Entry 8.
           4. Observe "elm.guide" part also works.
           5. Observe "icon" and "end" part works.

Reviewers: id213sin, herdsman, jpeg

Reviewed By: jpeg

Subscribers: conr2d, cedric, jpeg

Differential Revision: https://phab.enlightenment.org/D4962