Add TypeScript type-checking to all rules

We don't need to convert our JavaScript files to TypeScript, but by adding JSDoc comments with types and using the TypeScript [checkJs](https://www.typescriptlang.org/tsconfig#checkJs) option, we can get the benefits of type-checking. See this PR for an example and list of benefits: https://github.com/square/eslint-plugin-square/pull/723.