Font styling makes Calc slow

[Lorem Daijoh]

Tested on:

Ubuntu 20.04, Libreoffice 6.4.7.2
Ubuntu 21.10, Libreoffice 7.1.5.2

A Calc spreadsheet with random text on few columns and roughly every other row BOLDED is very slow to open and edit. Removing all BOLDING from the document makes it fast again.

Same effect can be achieved with font coloring. Likely other font styles too.

Other side effects include File, Edit and Tools menubar menus being very slow to open.

Test spreadsheet (~50kB, 4k rows) with both bolded and colored rows provided for testing. Takes about minute to load. File menu takes 10 seconds to open each time.

The last good version without this considerable slowdown is Libreoffice 6.4.6. Opens in few seconds. Menus are immediate.