MVC BeforeAction event needs changes in ASP.NET Core 3.0

[lmolkova]

In ASP.NET Core 3.0 Mvc events payloads have changed:

• they are now public types (but we probably can't use them as we don't depend on MVC packages)
• properties name now start with a capital letter

https://github.com/aspnet/AspNetCore/blob/09722d1ce59d4a7740451e065256ec62cbdb32a9/src/Mvc/Mvc.Core/src/Diagnostics/MvcDiagnostics.cs#L23

We only use BeforeAction event and we need to be case-insensitive or have different logic for 2.* vs 3.0+
https://github.com/microsoft/ApplicationInsights-aspnetcore/blob/develop/src/Microsoft.ApplicationInsights.AspNetCore/DiagnosticListeners/Implementation/HostingDiagnosticListener.cs#L763

[rynowak]

I'd suggest just being case-sensitive. That was the original design intent on our side.