Change the name of the MSTest.Runner

[OsirisTerje]

Summary

Change the name of the MSTest.Runner to Microsoft.Testing.Runner (or something else that is test framework agnostic.

Background and Motivation

The new MSTest.Runner is intended to also support the other frameworks, XUnit and NUnit, ref #2164

It is then very confusing and unfortunate to have this being named MSTest.Runner, as it is more of a Microsoft.Testing.Runner.

It also makes comments like this

We just need to provide enough new nice features for you to want to migrate to MSTest

in #2164 (comment)

confusing. Does the commenter mean that this is an attempt to convert all XUnit and NUnit users to move to use the MSTest framework or does he mean that he want users to use the misnamed MSTest.Runner instead of the current runners ? I prefer to believe it is the latter. If it is the former, well, the runner is not that important, the framework is.

Proposed Feature

Change the name of the MSTest.Runner to Microsoft.Testing.Runner (or something else that is test framework agnostic.

[Evangelink]

Thanks @OsirisTerje, we will review this name change request soon.

[Evangelink]

Docs website has been updated, this will take some time to flow to public but I will move forward by closing this task.