Add the flutter_js target as a dep to web_sdk. (flutter/engine#48814)

Currently, the `flutter_js` target is built as part of the flutter_web_sdk_archive target. However, it should also be built when doing the normal web_sdk, as that is what the monorepo builds (and does its own archiving).

engine/src/flutter/web_sdk/BUILD.gn

@@ -31,6 +31,7 @@ group("web_sdk") {
   deps = [
     ":flutter_ddc_modules",
     ":flutter_platform_dills",
+    "//flutter/lib/web_ui/flutter_js",
   ]
 }