Automate handling of added/modified indices on package upgrade

End goal:
A package developer should have to do zero work to handle addition of new indices in a new release of their package.

Placeholder from AppS/HS(Dev)Ops discussion today - could do something like:
In Initialize, capture the set of existing indices (in code) - might be empty.
In Activate, capture the set of modified indices (added/updated) then SetMapSelectibility to 0 for each of them.
Subject to command line flag (defaulting to "build them right now" but allowing deferral as well) call a new BuildIndices lifecycle phase that builds/rebuilds the new/modified indices then enables them for use.