LibDevTools+LibWebView: Implement getting document style sheets

Author: https://github.com/trflynn89
Commit: 0b86bcfba7
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3920

Libraries/LibDevTools/CMakeLists.txt

@@ -12,6 +12,7 @@ set(SOURCES
     Actors/PreferenceActor.cpp
     Actors/ProcessActor.cpp
     Actors/RootActor.cpp
+    Actors/StyleSheetsActor.cpp
     Actors/TabActor.cpp
     Actors/TargetConfigurationActor.cpp
     Actors/ThreadActor.cpp