Allow creating hyperlinks from one slide to another

[pscanf]

Possible workflow:

• select an element (text or otherwise)
• among the options for the element, there's the possibility to attach a hyperlink to it
• attach a hyperlink to another slide (this requires slides to be selectable via url)
• click on the hyperlink
• get sent to the linked slide

Notes:

• probably requires https://github.com/excalidraw/excalidraw/issues/1205