Ladybird/Android: Move common service functionality to a base class

Create LadybirdServiceBase to hold the standard "set resource dir" and
"init ipc sockets" service functionality that will be common between the
WebContent, RequestServer, and WebSocket services.

Refactor the handler class slightly to avoid the HandlerLeak lint by
making the class a static class inside the companion object and use a
WeakReference to the service instead of a strong one.

Ladybird/WebContent/CMakeLists.txt

@@ -55,7 +55,7 @@ else()
     if (ANDROID)
         target_sources(webcontent PRIVATE
           ../Android/src/main/cpp/WebContentService.cpp
-          ../Android/src/main/cpp/WebContentServiceJNI.cpp
+          ../Android/src/main/cpp/LadybirdServiceBaseJNI.cpp
         )
         target_link_libraries(webcontent PRIVATE android)
     endif()