Make a newly-installed version active if it's the only installed version

Tell us how we can improve Xcodes

Make a newly-installed version active if it's the only installed version.

Is your feature request related to a problem? Please describe.

No.

What would you like to see? How would you like it to work?

We currently do not automatically make versions active in any situation, and I think that's okay as 1) i'm not sure that all users would want to switch active versions in this situation 2) it's easy enough to do manually. In the case that there's only one version installed, though, I think all users would want it to be made active. The only situation I can think of that they might not want this is if they wanted the Command Line Tools to remain active, but those aren't currently a consideration of xcodes or Xcodes.app at all.

The user would have just been asked to install the helper for the post-install steps, so if the helper is not installed when Xcodes should automatically make the version active, maybe it should skip attempting this in order to not bug them about the helper again.

No files or tests are named in the issue. Start by tracing the post-install flow and helper-install handling; done means a newly installed version is automatically made active when it is the only installed version, without prompting again for a missing helper.