Link to issue number:

#13578

Summary of the issue:

Intermittent GC error "unreachable objects" caused by PR #13345.

Description of how this pull request fixes the issue:

The root cause was that we used to store TextInfo object inside Document, thus creating a cyclic reference. Such reference loops cannot be deleted by zeroing reference counter and can only be deleted by full GC sweep. I am not sure why NVDA prints warnings in this case.
This was fixed by not storing TextInfo in the first place. We now store last cell coordinates as lastRow/lastCol. Table cache is going to be valid as long as row/col of current selection are the same as stored lastRow/lastCol - and in this case we will be using trueRow/trueCol to compute next cell to preserve coordinates when navigating through merged cells.

Testing strategy:

Tested in HTML tables in both Chrome and Firefox.
Tested using explicit test case by @lukaszgo1 in #13578.

Known issues with pull request:

N/A

Change log entries:

N/A

Code Review Checklist:

• Pull Request description:
  • description is up to date
  • change log entries
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• API is compatible with existing add-ons.
• Documentation:
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English