Probing consumes a significant ammount of time at startup in the host. With changes introduced indotnet/runtime#50671, we move away from expensive file-accessing calls made by the host's probing logic and make them conditional upon whether any additional probing paths were passed to hostpolicy. This improves performance of anydotnet ... command as well as the time to main.

Note that by default the SDK generates a<app>runtimeconfig.dev.json when building an app, which ends up adding additional probing paths which are not necessary (all dependencies are included in the app folder which is probed first, related:#15210) -- causing the host to probe more than necessary and missing on any performance gains achieved by the above PR.

/cc@vitek-karas@brianrob