LibWebView: Move OutOfProcessWebView to a new LibWebView library

Also moves WebContentClient and the references to the generated IPC
descriptions, since they are all components of OutOfProcessWebView.

This patch has no functional changes.

Userland/Applications/Help/HelpWindow.gml

@@ -41,7 +41,7 @@
             }
         }
 
-        @Web::OutOfProcessWebView {
+        @WebView::OutOfProcessWebView {
             name: "web_view"
         }
     }