Implement DateEditor and DatetimeEditor for Tabulator

[philippjfr]

Builds on #2898 (i.e. should be rebased once that is merged)

[codecov]

Codecov Report

Merging #2899 (f265685) into master (7d418e9) will decrease coverage by 0.02%.
The diff coverage is 68.33%.

@@            Coverage Diff             @@
##           master    #2899      +/-   ##
==========================================
- Coverage   83.09%   83.07%   -0.03%     
==========================================
  Files         190      190              
  Lines       24640    24658      +18     
==========================================
+ Hits        20474    20484      +10     
- Misses       4166     4174       +8     

Impacted Files	Coverage Δ
panel/tests/widgets/test_tables.py	99.46% <ø> (ø)
panel/reactive.py	74.42% <63.46%> (-0.79%)	⬇️
panel/widgets/tables.py	85.17% <100.00%> (+0.14%)	⬆️
panel/tests/pane/test_plotly.py	98.77% <0.00%> (+0.61%)	⬆️

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