Replace List<T> with MyList<T> (#11649)

* change relative links

We prefer ~ - based links to samples, because those links are from another repository.

* Replace List with MyList

Fixes #7884

The `List<T>` example causes confusion with the .NET Standard type `System.Collections.Generic.List<T>`

Change the name of that type, update all references to the type name, and add a note to the .NET Standard type.

Depends on dotnet/samples#785

* Apply suggestions from code review

Co-Authored-By: BillWagner <[email protected]>

* fix reference link.

* fix typo in link.

Author: BillWagner