Add overlay between calendar and open simple editor

[ChristophWurst]

Is your feature request related to a problem? Please describe.

As a Nextcloud user I don't want other calendar elements to be clickable while the simple editor is open.

E.g.

1. Open my calendar with existing events
2. Click on event a -> see the simple editor for a
3. Click on event b -> see the simple editor for b

Describe the solution you'd like

1. Open my calendar with existing events
2. Click on event a -> see the simple editor for a
   3. I'm not able to click anything outside of the simple editor within the view of the calendar. This is similar to modals.
3. I'm not able to click anything outside the simple editor when in editing mode. (Discussed in the frontend channel)

Describe alternatives you've considered

#5513

Additional context

N/a

[nimishavijay]

Ideal solution:

• clicking anywhere outside of the editor when it is in edit mode does nothing (editor stays open in edit mode)
• clicking anywhere outside of the editor when it is in view mode closes the editor and does not open anything else