Fix dropdown closing

Fixes #2780 

This is an updated version of #2808. Instead of just setting `pointer-events: none` on the cursor, set it on the entire `CodeMirror-lines` element. This is the same thing that was done in the v2 branch.

There is one complication--inline editors are now children of the `CodeMirror-lines` div, so `pointer-events` need to be reset to `auto` for the inline editor div.