efl: Change non required constructors to @optional.
These constructors aren't checked for in the finalize step of the
initialization and may be given the @optional tag.
For C# this means they can be ommitted from the constructor call.
This also adds Efl.Ui.View.model as a constructor of
Efl.Composite_Model as the finalizer checks for it.
Test Plan: make check
Reviewers: segfaultxavi, zmike, bu5hm4n, cedric, felipealmeida
Reviewed By: segfaultxavi, cedric
Maniphest Tasks: T7673
Differential Revision: https://phab.enlightenment.org/D7855