efl: Change non required constructors to @optional.

efl: Change non required constructors to @optional.

Summary:
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.

Fixes T7673

Test Plan: make check

Reviewers: segfaultxavi, zmike, bu5hm4n, cedric, felipealmeida

Reviewed By: segfaultxavi, cedric

Tags: #efl, #do_not_merge

Maniphest Tasks: T7673

Differential Revision: https://phab.enlightenment.org/D7855