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 <[email protected]>
Reviewed-By: Weijia Wang <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: James M Snell <[email protected]>

.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',