Add Tabulator.on_click callback

[philippjfr]

For some use cases you need to know which exact cell was clicked on so we add a on_click callback. We also deprecate the on_button_click callback which was only introduced recently.

[codecov]

Codecov Report

Merging #3245 (a892f4f) into master (6d7c416) will decrease coverage by 0.31%.
The diff coverage is 46.15%.

@@            Coverage Diff             @@
##           master    #3245      +/-   ##
==========================================
- Coverage   83.11%   82.80%   -0.32%     
==========================================
  Files         193      193              
  Lines       25938    25427     -511     
==========================================
- Hits        21559    21054     -505     
+ Misses       4379     4373       -6     

Impacted Files	Coverage Δ
panel/widgets/tables.py	84.68% <45.45%> (-0.48%)	⬇️
panel/models/tabulator.py	94.25% <50.00%> (-1.26%)	⬇️
panel/auth.py	37.39% <0.00%> (-4.06%)	⬇️
panel/config.py	58.35% <0.00%> (-2.94%)	⬇️
panel/pane/ipywidget.py	48.57% <0.00%> (-2.78%)	⬇️
panel/io/reload.py	68.88% <0.00%> (-2.54%)	⬇️
panel/tests/template/test_manual.py	59.13% <0.00%> (-2.48%)	⬇️
panel/pane/plot.py	57.60% <0.00%> (-1.98%)	⬇️
panel/models/terminal.py	82.14% <0.00%> (-1.73%)	⬇️
panel/pane/streamz.py	68.57% <0.00%> (-1.70%)	⬇️
... and 100 more

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