Update ADVI interface to match AdvancedVI.jl

[Red-Portal]

This PR updates the internals of Turing to match the rebooted AdvancedVI.jl.

Breaking? Changes

The only change from the previous interface is that I propose to move the number of iterations from ADVI to vi.
That is, change

vi(model, ADVI(n_iter, n_mc), q)

to

vi(model, ADVI(n_mc), q, n_iter)

This is more consistent with the MCMC interface sample where the number of samples is supplied to sample not NUTS.

Dependencies

This currently depends on

• the purported reboot PR for AdvancedVI and
• the migration of Turing to the ADTypes interface in this PR.