Displays InfoBar for REF Error - but needs 2 UNDO

[ferdiga]

Change-Id: I750162d71a79f919b4416120f082c9ac47dad6f7
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/200345
Reviewed-by: Dan Williams dcbw@libreoffice.org
Tested-by: Jenkins
Reviewed-by: Patrick Luby guibomacdev@gmail.com

Deleting a referenced cell causes an #REF! error in the formula WITHOUT user feedback

• UNDO only possible during the current session
• after opening the file again - manual and often time consuming refactoring is necessary
• Collabora Online - the chances of breaking the formulas are greater because more users can change (delete) the code and it becomes an impossible task to find out who and when did what to break the sheet

Required user feed back

• Display DANGER info bar with cell reference of the first referencing cell and lost reference
• Remove Info bar on UNDO (and re check if 'REF! are gone ?)
• Make it thread safe using broadcast

Current status

• thread proof implementation using Broadcast

ToDo

• needs 2 UNDO clicks to revert, as the creation of the InfoBar is considered as own UNDO
• implement an option or automatic to check for dirty sheets with #REF! Errors

[github-actions]

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