Currently Compass uses ace-editor in a way that makes it a focus trap, meaning that when a user tabs into the aggregation stage editor input they are unable to use the keyboard to leave (except with undocumented option+tab). We should improve this accessibility issue by providing an aria description with the key a user can press to navigate out of the element.

I'm thinking we can add an `Escape` key handler which disables the ace editors `indent` and `outdent` commands until the ace editor is refocused. Similar to the example Sergey linked in COMPASS-4900: https://codemirror.net/examples/tab/
https://www.w3.org/TR/2016/WD-wai-aria-practices-1.1-20160317/#richtext
We'll then document this escape key handler using aria-label or similar.