`no-unreachable` should not be disabled

[benj-dobs]

The TypeScript compiler only enforces this check if explicitly configured to do so: https://www.typescriptlang.org/tsconfig#allowUnreachableCode

(Default behaviour is just to surface an editor warning.)

no-unreachable is disabled here:

eslint-config-airbnb-typescript/lib/shared.js

Line 282 in 766a2b9

'no-unreachable': 'off',

I think it would be more in-keeping with the spirit of this config to leave it enabled, rather than requiring users to have allowUnreachableCode: false in their tsconfig file to achieve the same behaviour.

[benj-dobs]

I've raised an issue for the ESLint docs too: eslint/eslint#18378