Improvements/Fixes

• PosInformatique.Testing.Databases.SqlServer target the .NET Standard 2.0 platform.
• PosInformatique.Testing.Databases.SqlServer.Dac target the .NET Core 6.0 and .NET Framework 4.6.2
• PosInformatique.Testing.Databases.SqlServer.EntityFramework target the .NET Core 6.0
• Reduce the dependencies to Entity Framework 6.0
• Reduce the dependencies of DACfx to a more earlier version.
• Add new method SqlServerDatabase.ExecuteScript() to execute T-SQL scripts.