DevTools Client - Simplify Strongly Typed Event handling (#3777)

* DevTools Client - Simplify Strongly Typed Event handling

Now it's only possible to register one System.Type per event.

- Remove RegisterEventHandler
- Add AddEventHandler and RemoveEventHandler
- Change constraint from DevToolsDomainEventArgsBase to EventArgs

https://github.com/cefsharp/CefSharp/issues/3666

* Changes were based on https://github.com/CefNet/CefNet.DevTools.Protocol

Add links to original source files

* Reset stream position

* AddEventHandler - Use GetOrAdd for Thread safety

* AddEventHandler - Fix double event handler registration for first call

* RemoveEventHandler - Remove IEventProxy when handler null