I am Neethu Mariya Joy, an undergraduate pursuing BE in Computer Science at BITS Pilani.
I've attempted to fix https://redmine.postgresql.org/issues/3083. Since the textarea resize feature is the default HTML feature, I have not changed it. Instead, I've added draggable borders to the wrapper which expands the textarea inside it.
I'm attaching my patch as bug3083.diff below as per the contribution guidelines.
Hope this helps. Thank you for your consideration!