csharp: Fix build and doc generation re beta stuff
When skipping beta items, make sure generated documentation does not try
to refer to beta stuff using see tags. Doing so would lead to warnings
when generating the xml doc file and as we now treat warnings as errors,
compilation would fail.
Instead of see tags, use a simple span with a suffix text explaining
said item is beta.
Reviewers: vitor.sousa, felipealmeida, segfaultxavi
Reviewed By: segfaultxavi
Tags: efl, #expertise_solutions
Differential Revision: https://phab.enlightenment.org/D9258