Rollback the EF Core 2.X content

Hi,

In my company, we have begun to migrate from .NET Framework to .NET, but it will take some time. Currently, we have many application in .NET Framework with ASP.NET Core 2.1 and Entity Framework 2.1.

But some very useful information for EF Core 2.1 was removed in #4171. For example, today I don't remember that is the inheritance model is available in EF Core 2.1. Then I consult the doc, but the information is missing.

EF Core 2.1 is always supported on .NET Framework as indicated in this page :
https://learn.microsoft.com/en-us/ef/core/what-is-new/
> * EF Core 2.1 will continue to be supported when used with ASP.NET Core 2.1 on .NET Framework only. See [ASP.NET Support Policy](https://dotnet.microsoft.com/platform/support/policy/aspnet) for details.

Can you rollback the deleted content about EF Core 2.X?
Maybe you can do something like the ASP.NET Core where is possible to select a version.

Similar dotnet/AspNetCore.Docs#25171