mono-docs: Allow derived classes to have external examples

mono-docs: Allow derived classes to have external examples

Summary:
You can now have external example files for derived classes (Efl.Ui.Button.SetText)
as well as for base classes (Efl.IText.SetText).
If both files are present, both examples are embedded in the docs. The more
examples the better!

Examples for classes in-between the hierarchy (Efl.Ui.Widget.SetText) are not
picked up. Might be worth examining in the future.

Test Plan:
Create example files for both `Efl.Ui.Button.AutorepeatEnabled.cs` and `Efl.Ui.IAutorepeat.AutorepeatEnabled.cs`.
You should see both examples appearing in the docs.

Reviewers: lauromoura, vitor.sousa

Reviewed By: vitor.sousa

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D8597