[Test Framework] Move tests framework to netcoreapp3.1 from netcoreapp3.0

[vzarytovskii]

Need to move for both F# and C#.
Should probably consume needed framework files from the Test.Utilities project, and provide when using Roslyn APIS

[vzarytovskii]

Can be started, once #9801 is merged.

[vzarytovskii]

Should be fixed in #9870