[Breaking] Remove Legacy Bootstrapper

[brianlagunas]

Description of Change

I am officially removing the old, legacy bootstrapper class from Prism. There are two upgrade paths for developers using the old legacy UnityBootstrapper.

• Switch to using the PrismApplication class
• Upgrade your current UnityBootstrapper to the new PrismBootstrapper

Bugs Fixed

• [Breaking] Remove Legacy Bootstrapper #2177

API Changes

List all API changes here (or just put None), example:

Removed:

• UnityBootstrapper
• DryIocBootstrapper

Behavioral Changes

This is a major breaking change. Upgrading to the PrismApplication or PrismBootstrapper will not change any behavior in your application.

PR Checklist

• Has tests (if omitted, state reason in description)
• Rebased on top of master at time of PR
• Changes adhere to coding standard

[dansiegel]

Generally it looks good to me. I just would fix the manager.Run() call since this would introduce a bug as the ContainerExtensions expects to be able to resolve a type or throw an exception.