feat: add type declaration file (#279)

* Add type declaration file

Hand roll a type declaration file for `flat.js` that accurately reflects
the exported plugin. This resolves type errors when attempting to use
`globals` and `recommended` configs in type-checked eslint configs and
also aids in autocomplete when typing (as in keyboard button press, not
"does it satisfy expected type") properties of the plugin.

* (Revisions) Add type declaration file

Update code style from review

Co-authored-by: Mike McCready <[email protected]>

---------

Co-authored-by: Mike McCready <[email protected]>

Author: mdmower-csnw

lib/flat.d.ts

@@ -0,0 +1,12 @@
+import type { ESLint, Linter } from 'eslint'
+
+declare const plugin: {
+  meta: { name: string, version: string }
+  configs: {
+    globals: Linter.Config<Linter.RulesRecord>
+    recommended: Linter.Config<Linter.RulesRecord>
+  }
+  rules: NonNullable<ESLint.Plugin['rules']>
+}
+
+export = plugin