Drupal core ESLint validation expanded to check camel case

As of Drupal 8.5, Drupal core's ESLint syntax checking enforces more rules, for more cohesive JavaScript. For a "preview" of what's to come, see the JavaScript clean-up issue tag.

camelcase

Variables should now use camelCase naming conventions, as opposed to underscore_separated naming conventions; for example:

-        const element_settings = {};
+        const elementSettings = {};