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

#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

Author: amaitland

CefSharp/CefSharp.csproj

@@ -88,7 +88,6 @@
     <Compile Include="DevTools\DevToolsClient.cs" />
     <Compile Include="DevTools\DevToolsClient.Generated.cs" />
     <Compile Include="DevTools\DevToolsClientException.cs" />
-    <Compile Include="DevTools\DevToolsEventHandlerRegistration.cs" />
     <Compile Include="DevTools\DevToolsMethodResponseContext.cs" />
     <Compile Include="DevTools\DevToolsDomainBase.cs" />
     <Compile Include="DevTools\DevToolsDomainEntityBase.cs" />
@@ -97,8 +96,10 @@
     <Compile Include="DevTools\DevToolsDomainResponseBase.cs" />
     <Compile Include="DevTools\DevToolsEventArgs.cs" />
     <Compile Include="DevTools\DevToolsMethodResponse.cs" />
+    <Compile Include="DevTools\EventProxy.cs" />
     <Compile Include="DevTools\Headers.cs" />
     <Compile Include="DevTools\IDevToolsClient.cs" />
+    <Compile Include="DevTools\IEventProxy.cs" />
     <Compile Include="DevTools\MemoryDumpConfig.cs" />
     <Compile Include="Enums\CompositionUnderlineStyle.cs" />
     <Compile Include="Enums\CookiePriority.cs" />