Use and support NET 8 SDK artifacts output

[lahma]

Use the new NET 8 SDK artifacts output layout feature which consolidates bin and obj folders under artifacts directory. Need to move Directory.Build.props to root level for proper configuration.

To remove old cruft, might be good idea to run locally in solution root directory:

Get-ChildItem .\ -include bin,obj -Recurse | foreach ($_) { remove-item $_.fullname -Force -Recurse }

This also improves the project metadata querying by trying to use the new CLI-based metadata querying , basically obj folder can now be anywhere and no need to give extensions path like before (for artifacts output enabled projects it would always fail). New retrieval should be faster too. If NET 8 SDK is not present, old logic will be used.

[RicoSuter]

lgtm. thanks