Meta: Port recent LibWeb and LibJS changes to gn build

This ports the following commits:
a8587fe54e14e106b03a2c1c47829962078cc9ba
9d7215c636eebfb03c0f9dc6e5be25d66e82d1b5

Meta/gn/secondary/Userland/Libraries/LibJS/BUILD.gn

@@ -165,7 +165,6 @@ shared_library("LibJS") {
     "Runtime/IteratorConstructor.cpp",
     "Runtime/IteratorHelper.cpp",
     "Runtime/IteratorHelperPrototype.cpp",
-    "Runtime/IteratorOperations.cpp",
     "Runtime/IteratorPrototype.cpp",
     "Runtime/JSONObject.cpp",
     "Runtime/JobCallback.cpp",

Meta/gn/secondary/Userland/Libraries/LibWeb/CSS/StyleValues/BUILD.gn

@@ -36,6 +36,7 @@ source_set("StyleValues") {
     "NumberStyleValue.cpp",
     "OverflowStyleValue.cpp",
     "PlaceContentStyleValue.cpp",
+    "PlaceItemsStyleValue.cpp",
     "PositionStyleValue.cpp",
     "RadialGradientStyleValue.cpp",
     "RectStyleValue.cpp",