LibWebView: Implement a WebView-based Inspector client

This is modeled after a similar implementation for the JS console.

This client takes over an inspector WebView (created by the chrome) to
create the inspector application. Currently, this application includes
the DOM tree and accessibility tree as a first pass. It can later be
extended to included the style tables, the JS console itself, etc.

Userland/Libraries/LibWebView/Forward.h

@@ -14,6 +14,7 @@ class ConsoleClient;
 class CookieJar;
 class Database;
 class History;
+class InspectorClient;
 class OutOfProcessWebView;
 class ViewImplementation;
 class WebContentClient;