message: [tests] Add lint rule to prevent substr()
  Follow up to so we don't accidentally add substr() again
diff: "es6": true
  },
  "rules": {
  + "no-restricted-syntax": [
  + "warn",
  + "WithStatement",
  + {
  + "message": "substr() is deprecated, use slice() or substring() instead",
  + "selector": "MemberExpression > Identifier[name='substr']"
  + }
  + ],
  "require-atomic-updates": 0,
  "@typescript-eslint/ban-ts-comment": 0,
  "@typescript-eslint/camelcase": 0,
  