Various changes to improve Tabulator robustness

[philippjfr]

Two fixes to improve Tabulator robustness:

1. Guard this.model.children look-ups since, when empty it sometimes appears to be an object rather than a Map.
2. Track scrolling state more robustly and do not run resize handler while scrolling (this was triggering tons of re-renders)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.19%. Comparing base (d57d393) to head (3209f77).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7275      +/-   ##
==========================================
- Coverage   82.19%   82.19%   -0.01%     
==========================================
  Files         337      337              
  Lines       50363    50363              
==========================================
- Hits        41398    41394       -4     
- Misses       8965     8969       +4     

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