Ensure unhiding Tabulator columns renders cells correctly

[philippjfr]

Fixes #4103

[codecov]

Codecov Report

Merging #4119 (b3e1ef6) into master (fc207d6) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4119   +/-   ##
=======================================
  Coverage   83.56%   83.57%           
=======================================
  Files         223      223           
  Lines       33262    33268    +6     
=======================================
+ Hits        27797    27804    +7     
+ Misses       5465     5464    -1     

Flag	Coverage Δ
ui-tests	37.59% <100.00%> (+0.03%)	⬆️
unitexamples-tests	74.60% <5.55%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
panel/tests/ui/widgets/test_tabulator.py	99.08% <100.00%> (+0.11%)	⬆️
panel/io/reload.py	69.56% <0.00%> (-2.18%)	⬇️
panel/tests/util.py	89.21% <0.00%> (-2.05%)	⬇️
panel/tests/command/test_serve.py	83.95% <0.00%> (-1.42%)	⬇️
panel/template/base.py	76.45% <0.00%> (-0.19%)	⬇️
panel/io/state.py	69.65% <0.00%> (-0.17%)	⬇️
panel/io/jupyter_server_extension.py	0.00% <0.00%> (ø)
panel/pane/idom.py	28.36% <0.00%> (+0.19%)	⬆️
panel/tests/conftest.py	88.79% <0.00%> (+0.38%)	⬆️
... and 2 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more