Update VisualStudio.gitignore to ignore NuGet Symbol Packages (#3041)

This is to ignore the new Nuget Symbol Packages, which are now the recommended approach for debug symbols of public NuGet packages.
https://docs.microsoft.com/en-us/nuget/create-packages/symbol-packages-snupkg

Author: alefranz

VisualStudio.gitignore

@@ -185,6 +185,8 @@ PublishScripts/
 
 # NuGet Packages
 *.nupkg
+# NuGet Symbol Packages
+*.snupkg
 # The packages folder can be ignored because of Package Restore
 **/[Pp]ackages/*
 # except build/, which is used as an MSBuild target.