Add a function to facilitate projections using TMB simulate()

[seananderson]

Inspiration in VAST: https://github.com/James-Thorson-NOAA/VAST/blob/7a9a3f7b84227fb41ab027ea3312df13c2035ff6/R/project_model.R

Can probably build this off sdmTMB_simulate(). Requires extending the parameter object and re-running MakeADFun, then simulate.

Faster than if done during fitting with extra_time.