tools: stricter no-undef eslint rule

By default eslint does not validate variables that are placed in a
typeof check.

PR-URL: #19926
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

.eslintrc.js

@@ -185,7 +185,7 @@ module.exports = {
     'no-this-before-super': 'error',
     'no-throw-literal': 'error',
     'no-trailing-spaces': 'error',
-    'no-undef': 'error',
+    'no-undef': ['error', { typeof: true }],
     'no-undef-init': 'error',
     'no-unexpected-multiline': 'error',
     'no-unreachable': 'error',