[BREAKING] Clean up API for create inner model

[blegat]

It's a bit counter intuitive to still add caches and bridges when the user explicitly give an instantiated model. I guess the use case is the DualizableModel but maybe we don't need this. We're using a UniversalFallback on top of it anyway so what's the use for it instead of just MOI.Utilities.Model ?

[blegat]

This is consistent with ParametricOptInterface which does some magic if it takes an optimizer constructor as argument but when it takes an instantiated optimizer, it does not modify it.

[joaquimg]

Interesting,
Should we document this pattern in MOI docs?

[blegat]

Interesting, Should we document this pattern in MOI docs?

Yes, I think we should discuss this, and it should also go in parallel with the layer design that @odow suggested in
jump-dev/JuMP.jl#4014 (comment)
In the meantime, we can try to see if we can simplify the logic of each layer. For POI, we could improve MatrixOfConstraints to get rid of
https://github.com/jump-dev/ParametricOptInterface.jl/blob/2219828f43a81268a3c0b4bc787b1ea48a9e768f/src/ParametricOptInterface.jl#L304-L317