Allow users to clear NuGet cache from within Visual Studio

Package authors, consumers.

Button existed on previous version of NuGet. This work is related to enabling locals command in dotnet cli.

Add a button to the VS Package Manager options which calls into the LocalsCommandRunner.cs from NuGet.Core.CommandLine.Commands. The call is similar as nuget locals -clear all from nuget CLI or dotnet nuget locals --clear all from dotnet CLI.

The result is displayed on a popup/message box.

The result will be displayed in a label below the Clear cache button along with the time stamp of completion of the operation. The error messages also contain a link to a help page. The screenshots below have been updated.