Close all documents dialogue overflows with many open documents

Reproduction

• Open many documents with File->New…
• Try to close them all with File->Close All
• Observe that it is not possible to click the OK button as it is off the screen

Relevant code

https://github.com/GraphiteEditor/Graphite/blob/b1b372f1d68854d686d1c8a9ff1c4a30660420a2/editor/src/messages/dialog/simple_dialogs/close_all_documents_dialog.rs#L32-L39