Issue #3378890 by Wim Leers, mikesimmons, smustgrave, pmkanse, witeksocha: Add...

Issue #3378890 by Wim Leers, mikesimmons, smustgrave, pmkanse, witeksocha: Add the "Show Blocks" functionality that existed in CKEditor 4 and was added to CKEditor 5 38.1.0

(cherry picked from commit 116c87e4)