[a11y] 9.1.3.2 Sensible sequence

[tschiebel]

audit: https://infinite.owncloud.com/s/PnaAukHGGsLnrMM

https://bitvtest.de/pruefschritt/bitv-20-web/bitv-20-web-9-1-3-2-sinnvolle-reihenfolge

Personal

• If the custom tooltip "Share with people" in the "Share" section
  is open, it is still possible to access the content behind the tooltip using the screen reader.
  behind the tooltip using the screen reader. This should be prevented.
  

• The days of the week in the date picker elements are output by screen readers as
  individual letters. For this reason, it is recommended to make them
  invisible for screen reader users.

Shares

• See comments on Personal

Spaces

• If the user-defined tooltip "Add members to this Space" is open in the
  "Members" area is open, it is still possible to access the content behind the tooltip using the
  screen reader to access the content behind the tooltip. This should
  be prevented. A similar problem also affects user-defined tooltips "Please select how
  access is granted" and "Access details".

• The days of the week in the date picker elements are displayed by screen readers as
  as individual letters. For this reason, it is recommended to make them invisible for screen reader users.

[JammingBen]

The date picker violations should be obsolete with the native browser picker we use nowadays. The other issues have been fixed with #11574.