Meta: Port recent changes to the GN build

a1f4d1875e1c157218f7a15e27adce70d3375f78

Meta/gn/secondary/Userland/Libraries/LibWeb/Internals/BUILD.gn

@@ -3,6 +3,7 @@ source_set("Internals") {
   deps = [ "//Userland/Libraries/LibWeb:all_generated" ]
   sources = [
     "Inspector.cpp",
+    "InternalAnimationTimeline.cpp",
     "Internals.cpp",
   ]
 }

Meta/gn/secondary/Userland/Libraries/LibWeb/idl_files.gni

@@ -223,6 +223,7 @@ standard_idl_files = [
   "//Userland/Libraries/LibWeb/HTML/WorkerLocation.idl",
   "//Userland/Libraries/LibWeb/HTML/WorkerNavigator.idl",
   "//Userland/Libraries/LibWeb/Internals/Inspector.idl",
+  "//Userland/Libraries/LibWeb/Internals/InternalAnimationTimeline.idl",
   "//Userland/Libraries/LibWeb/Internals/Internals.idl",
   "//Userland/Libraries/LibWeb/IntersectionObserver/IntersectionObserver.idl",
   "//Userland/Libraries/LibWeb/IntersectionObserver/IntersectionObserverEntry.idl",