Make tinymce work with TS 4.4 DOM (#54055)
Make tinymce work with TS 4.4 DOM (#54055)

UndoManager refers to DocumentEvent, which is removed in TS 4.4's
version of the DOM. I replaced it with Event, since I don't think it was
meant to be DocumentEvent in the first place, based on DocumentEvent's
definition as an event factory.

microsoft/TypeScript#44684
markogresak/DefinitelyTyped