Desktop: Fixes #9953, #9948: Rich text editor: Fix context menu not shown in some cases

[personalizedrefrigerator]

Summary

The logic for showing a context menu in the rich text editor was incorrect in two cases:

• The editor was zoomed in
• The editor was hidden behind another element.

This is fixed by adjusting the logic that accounts for the page's current zoom and using document.elementFromPoint.

Fixes #9953 and #9948.

Testing

1. Create a note with a large amount of text.
2. Open it in the rich text editor.
3. Attach an image.
4. Zoom in such that the image is near the bottom/right edge of the screen.
5. Right click along the right and bottom edges of the screen. Verify that the correct context menu is shown.
6. Add a code block such that the code block dialog is open.
7. Right click in the part of the code block dialog that overlaps the rich text editor. Verify that a right click menu is shown and can be used to paste text.

This has been tested successfully on Ubuntu 23.10.

Screencast.from.2024-02-16.13-54-24.webm