Change Roslyn to target netcoreapp3.1 when building .NET Core assets.

Previously the code targetted a mix of netcoreapp2.1 and netcoreapp3.0.
The mix is due to default interfaces only being supported on
netcoreapp3.0 and hence our testing needed to use that. Yet at the same
time we were required to ship the compiler in SDKS that targetted
netcoreapp2.1. Now we can universally target netcoreapp3.1.

This reverts commit 27ecd825.

* Rework build definitions to accept VS optprof drop

* Update dependencies from https://github.com/dotnet/arcade build 20191205.2

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19605.2

* Pack Content for anlyzer packages

* Skip failing C# REPL integration tests.

After CI image was updated with 16.4 Preview 5 some REPL tests started
failing consistently. https://github.com/dotnet/roslyn/issues/40160

* Skip additional test

Editor team recently added a new GetSuggestedActions API overload that allows providing a more detailed operation scope message. This PR moves us to that API for Roslyn suggested actions. We now display the name of the executing analyzer/fixer/refactoring when user hits Ctrl + Dot to bring up the light bulb. This should help the users identify the slow extension and help us in improving performance of our analyzers/fixers/refactorings.

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19555.7

This removes the hard dependency on the editor packages so we can
still support loading in 16.3. The unit tests must be disabled that
depend on the new support, but everything else will continue to
function.

Also fix violations from newly added rules.

This reverts commit 6880a46e.

packages

Delete a bunch of code on Roslyn side, which is no longer necessary as we don't own the column anymore.
I have also cleanup up some code in this space for newly added ContainingType and ContainingMember columns.

Use the latest flow analysis utilities package