[Breaking][v4] Assembly version shouldn't be fixed to 14.0.0.0

[Youssef1313]

Both test framework and adapter set UseAssemblyVersion14 to true.

https://github.com/microsoft/testfx/blob/7b0d5d1c5049a2a485586b45bce5a98305e3d300/Directory.Build.targets#L10-L11

We shouldn't do that anymore, and MSTest assemblies should be properly versioned, similar to MTP assemblies.

This means that in v4, we will have to use a lower version (4.x) instead of 14.x, which may also be problematic that a newer version of the assembly is actually using an older version number. Thus, I also think it's safest to rename the assembly altogether.

• Instead of Microsoft.VisualStudio.TestPlatform.TestFramework, we simply use MSTest.TestFramework
• Instead of Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter, we simply use MSTest.TestAdapter.

NOTE: I'm suspecting that fixing the version to 14.0.0.0 may be causing issues on .NET Framework when dealing with GAC.

[Evangelink]

When working on v3 I was told it was likely going to cause some issue on VS but without any example or explanations. Because I was just starting to get familiar with the codebase, I decided to avoid some more conflicts but it did caused quite a lot of unexpected other kind of issues with VSTEst

[Youssef1313]

As other test frameworks have proper assembly versioning, if this ever caused issues, I won't consider it an MSTest issue.