Use CodeMirror instead of Ace

[luizbills]

Pros

• CodeMirror is bundled directly on WordPress.

Cons

• Maybe some breaking change (I don't know yet).

[luizbills]

Useful links:

• CodeMirror docs: https://codemirror.net/docs/ref/
• https://developer.wordpress.org/reference/functions/wp_enqueue_script/#default-scripts-and-js-libraries-included-and-registered-by-wordpress