[Feature] Add offset backlink indicator icons from context menu

[RyotaUshio]

Sometimes we'd want to add a comment that isn't necessarily tied/bounded to a specific text selection. In that case, it would come in handy to have a context menu like "Add backlink icon" shown when right-clicking outside of text in PDF.

Current workaround: Zoom in & scroll to locate the upper-left corner of the viewer in the exact position where I want to place the icon, then run the command "Copy link to current page view" and paste the link to some note.

Screen.Recording.2024-05-01.at.6.48.07.mov