Custom eslint rule for disallowing cross-package references

Summary:
Added infra for writing and using custom eslint rules and created a rule for disallowing cross-package file imports. Such imports are anti-pattern and they also break standalone plugin bundling.

We still have a bunch of places where Flipper core references code directly from plugins. I've ignored these places for now and added task T71355623 to revisit them.

Reviewed By: passy

Differential Revision: D22998955

fbshipit-source-id: d04cff8fc115ba1300a7e6830306ec134046e927

desktop/eslint-plugin-flipper/src/index.ts

@@ -0,0 +1,18 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import noRelativeImportsAcrossPackages, {
+  RULE_NAME as noRelativeImportsAcrossPackagesRuleName,
+} from './rules/noRelativeImportsAcrossPackages';
+
+module.exports = {
+  rules: {
+    [noRelativeImportsAcrossPackagesRuleName]: noRelativeImportsAcrossPackages,
+  },
+};