build: forbid using TypeScript enums using eslint

[TypeScript enums][1] are an unusual TypeScript feature, because it's
one of the only features that is "not a type-level extension of
JavaScript".

This means TypeScript generates custom code for enums, which can cause a
bunch of issues, especially as this custom code can be built differently
depending on which bundler you use, and because of this, many people
discourage the use of enums:

- [The Dangers of TypeScript Enums][2]
- [Tidy TypeScript: Prefer union types over enums][3]
- [TypeScript: Handbook - Enums # Objects vs Enums][4]

I've added an ESLint rule that forbids TypeScript enums, as in most
cases, it's better to use string literals instead, e.g. like
`type a = "a" | "b" | "c";`.

[1]: https://www.typescriptlang.org/docs/handbook/enums.html#string-enums
[2]: https://dev.to/azure/the-dangers-of-typescript-enums-55pd
[3]: https://fettblog.eu/tidy-typescript-avoid-enums/
[4]: https://www.typescriptlang.org/docs/handbook/enums.html#objects-vs-enums

.eslintrc.cjs

@@ -123,6 +123,14 @@ module.exports = {
       files: ['*.{ts,tsx}'],
       plugins: ['tsdoc'],
       rules: {
+        'no-restricted-syntax': [
+          'error',
+          {
+            selector: 'TSEnumDeclaration',
+            message:
+              'Prefer using TypeScript union types over TypeScript enum, since TypeScript enums have a bunch of issues, see https://dev.to/dvddpl/whats-the-problem-with-typescript-enums-2okj',
+          },
+        ],
         'tsdoc/syntax': 'error',
       },
     },