csharp: Refactor annotation selection function

Summary:
Better names to convey their intent and formatting.

Removing the hardcoded return from them will also free the return list
to be used for @out parameters as they have similar semantics to
return, different from regular @in parameters. This change in
behavior will come in a future commit, and explains why are are keeping
both lists for now despite being essentially the same.

Ref T8515

Test Plan: Run existing tests

Reviewers: felipealmeida, brunobelo, jptiz, YOhoho

Reviewed By: jptiz

Subscribers: cedric, reviewers, committers

Tags: efl

Maniphest Tasks: T8515

Differential Revision: https://phab.enlightenment.org/D10827