csharp: Respect beta for implementable functions

csharp: Respect beta for implementable functions

Summary:
Build fix (remove warnings)

Instead of returning the beta functions in the vector and relying on
function generators to skip them, filter them out when filling the
implementable methods vector.

This will make the code return the actual number of implementable
function, skipping some unused fields in places like the NativeMethods
implementations.

Depends on D9258

Reviewers: vitor.sousa, felipealmeida, segfaultxavi

Reviewed By: vitor.sousa

Subscribers: cedric, #reviewers, #committers

Tags: #efl, #expertise_solutions

Differential Revision: https://phab.enlightenment.org/D9259