Mark effect list fields as old

And `subtreeTag` as new.

I didn't mark `lastEffect` because that name is also used by the
Hook type. Not super important; could rename to `lastEffect_old` but
idk if it's worth the effort.

Author: acdlite

.eslintrc.js

@@ -99,7 +99,18 @@ module.exports = {
     'react-internal/warning-args': ERROR,
     'react-internal/no-production-logging': ERROR,
     'react-internal/no-cross-fork-imports': ERROR,
-    'react-internal/no-cross-fork-types': ERROR,
+    'react-internal/no-cross-fork-types': [
+      ERROR,
+      {
+        old: [
+          'firstEffect',
+          'nextEffect',
+          // Disabled because it's also used by the Hook type.
+          // 'lastEffect',
+        ],
+        new: ['subtreeTag'],
+      },
+    ],
   },
 
   overrides: [