pdf.js: [Regression] Text-selection boxes visually overlap after PR 17533

Attach (recommended) or Link to PDF file here: https://github.com/mozilla/pdf.js/blob/master/test/pdfs/pdf.pdf.link

(This can be reproduce even with tracemonkey.pdf, but it’s less pronounced since the lines don’t overlap as much.)

Configuration:

• Web browser and its version: Firefox 123.0a1
• Operating system and its version: Windows 11
• PDF.js version: 5d2e7cf3fcac1d0536003369ab3163b006539bfa, i.e. PR #17533
• Is a browser extension: N/A

Steps to reproduce the problem:

1. Select text, and look at the intersection between different text-selection boxes.

What is the expected behavior? (add screenshot) The intersection should not be visible, as previously:

What went wrong? (add screenshot) The intersection is visible:

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension): N/A

/cc @calixteman