Pulling out of #8650 for readability.

Trying to clean this up to simplify extensions in the future. This is not a strict refactor, there are behavioral changes here.

• Adds some structs for managing state.
• Addresses some likely inconsistent behavior for weird edge-cases.
  • We fill platform information before checking if a request is satisfied.
  • We error earlier if we can't find a download for the request, i.e., even if you somehow have it installed.
  • Only reports versions as uninstalled if a download actually replaces them.
• Moves some of the default output to tracing messages.
• Even if an installation was already satisfied, we'll check that it is setup properly