Escape Should Blur FEEL Editor Without Closing Context Menu

[philippfromme]

The context menu component used by the input expression editor closes on Esc (cf. https://github.com/bpmn-io/table-js/blob/master/src/features/context-menu/components/ContextMenuComponent.js#L208). There is currently no way to prevent this behavior. When the FEEL editor is focused, pressing Esc should blur the editor but not close the context pad.

Follow-up to #770,

[barmac]

This will probably need some changes in table-js.