eolian-cxx: Add property_def

eolian-cxx: Add property_def

Summary:
While individual getters and setters are added to the list of methods of
a class, property_def will hold them as a pair.

This will help defining accessors like C#'s where they're grouped.

Also update some eolian-cxx tests that were commented out.

Depends: D7262

Test Plan: run eolian-cxx tests

Reviewers: vitor.sousa, felipealmeida

Reviewed By: vitor.sousa

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D7389