Move all "SLNS" that are only relevant for CI or specific scenarios to a separate folder

[PureWeen]

Description

• It's too confusing for users coming into our repository to have a slnf called "Microsoft.Maui.Samples.slnf". This is a solution that will only build if you follow the instructions here.
• The only solutions in the root should be the ones relevant to working MAUI
  • We could take this further and move all solutions out to separate directoroes enforcing the requirement to run the cake scripts in order to build the MAUI repository
  • We could also find a solution so that we aren't required to build the build tasks before opening the MAUI SLN. With Xamarin.Forms we checked in all the build task binaries. This might be too heavy of an operation now with now workloads/net7 change and the fact that we have resizetizer.

[Eilon]

If the SLN[F]'s are really only for build/CI stuff, definitely let's move them to a sub-folder.