Meta: Port 78e1defbfe to gn build

Author: https://github.com/ADKaster
Commit: https://github.com/SerenityOS/serenity/commit/777fb44bb0

Meta/gn/secondary/Ladybird/BUILD.gn

@@ -14,6 +14,7 @@ moc_qt_objects("generate_moc") {
   sources = [
     "BrowserWindow.h",
     "ConsoleWidget.h",
+    "EventLoopImplementationQtEventTarget.h",
     "InspectorWidget.h",
     "LocationEdit.h",
     "ModelTranslator.h",
@@ -81,6 +82,7 @@ executable("ladybird_executable") {
     "BrowserWindow.cpp",
     "ConsoleWidget.cpp",
     "EventLoopImplementationQt.cpp",
+    "EventLoopImplementationQtEventTarget.cpp",
     "HelperProcess.cpp",
     "InspectorWidget.cpp",
     "LocationEdit.cpp",

Meta/gn/secondary/Ladybird/WebContent/BUILD.gn

@@ -5,6 +5,7 @@ moc_qt_objects("generate_moc") {
   sources = [
     "//Ladybird/AudioCodecPluginQt.h",
     "//Ladybird/AudioThread.h",
+    "//Ladybird/EventLoopImplementationQtEventTarget.h",
     "//Ladybird/RequestManagerQt.h",
   ]
 }
@@ -48,6 +49,7 @@ executable("WebContent") {
     "../AudioCodecPluginQt.cpp",
     "../AudioThread.cpp",
     "../EventLoopImplementationQt.cpp",
+    "../EventLoopImplementationQtEventTarget.cpp",
     "../FontPlugin.cpp",
     "../HelperProcess.cpp",
     "../ImageCodecPlugin.cpp",