Fix require('ReactFeatureFlags') in eslint-plugin-react-hooks www build (#36243)

PR #35951 added FB_WWW_DEV builds for eslint-plugin-react-hooks to get
www-specific feature flag values. However, the FB_WWW build uses the
full ReactFeatureFlags.www.js fork, which contains:

  const dynamicFeatureFlags = require('ReactFeatureFlags');

This is a www Haste module that only exists in the www runtime. Rollup
can't tree-shake CJS require() calls (they're assumed side-effectful),
so the bare require('ReactFeatureFlags') survives in the build output
even though the eslint plugin only uses the static eprh_* exports.

When the built artifact is synced to www at
scripts/lint/eslint/rules/eslint-plugin-react-hooks/index.js, Node.js
fails with "Cannot find module 'ReactFeatureFlags'" because Haste
modules aren't available in the Node.js lint environment.

Create a dedicated fork (ReactFeatureFlags.eslint-plugin.www.js) that
exports only the static eprh_* flags with www values, without the
require('ReactFeatureFlags') dependency. Wire it up in forks.js for the
eslint-plugin-react-hooks entry point.

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Co-authored-by: Eugene Choi <eugenechoi@meta.com>

scripts/rollup/forks.js

@@ -163,6 +163,14 @@ const forks = Object.freeze({
               `Unexpected entry (${entry}) and bundleType (${bundleType})`
             );
         }
+      case 'eslint-plugin-react-hooks/src/index.ts':
+        switch (bundleType) {
+          case FB_WWW_DEV:
+          case FB_WWW_PROD:
+          case FB_WWW_PROFILING:
+            return './packages/shared/forks/ReactFeatureFlags.eslint-plugin.www.js';
+        }
+        return null;
       case 'react-test-renderer':
         switch (bundleType) {
           case RN_FB_DEV: