eolian_mono: Generate proper doc refs for Constants

eolian_mono: Generate proper doc refs for Constants

Summary:
Support for global constant variables has been recently added to the C# bindings.
This patch fixes doc references so they use the proper name.
This brings the mono doc warnings from 71 down to 29.

Depends on D8048

Test Plan:
Just build and see less doc warnings when building the C# bindings.
Also, doc refs to constants are links now.

Reviewers: lauromoura, vitor.sousa

Reviewed By: lauromoura

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D8051