Ensure Tabulator redraw is called after full render

[philippjfr]

There were some major issues with the logic responsible for ensuring that the Tabulator was redrawn. In fact the logic was specifically skipping redraws if this.tabulator != null, so we never triggered the redraw at all since this completely incorrect PR 3 months ago: #6930

Some additional improvements we make here:

• Do not trigger a redraw, while another is in process (this could happen because a redraw can trigger a resize which triggers another redraw)
• We do not trigger a initial redraw until the root.has_finished (i.e. the page is fully rendered).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.18%. Comparing base (1e8827b) to head (68ecf58).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7305      +/-   ##
==========================================
- Coverage   82.19%   82.18%   -0.01%     
==========================================
  Files         337      337              
  Lines       50380    50394      +14     
==========================================
+ Hits        41411    41418       +7     
- Misses       8969     8976       +7     

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