Implement support for Vega events

[philippjfr]

Implements #2365

[codecov]

Codecov Report

Merging #2592 (1304c3d) into master (d6b315f) will decrease coverage by 0.00%.
The diff coverage is 87.27%.

@@            Coverage Diff             @@
##           master    #2592      +/-   ##
==========================================
- Coverage   83.12%   83.12%   -0.01%     
==========================================
  Files         190      190              
  Lines       24900    24953      +53     
==========================================
+ Hits        20697    20741      +44     
- Misses       4203     4212       +9     

Impacted Files	Coverage Δ
panel/io/callbacks.py	66.66% <ø> (ø)
panel/models/vega.py	88.00% <75.00%> (-6.12%)	⬇️
panel/pane/vega.py	83.33% <88.88%> (+0.26%)	⬆️
panel/tests/pane/test_base.py	84.31% <100.00%> (+0.31%)	⬆️

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[maximlt]

Really liking this API! 👍

The description of debounce may need a few more words, or a link to a source explaining what that is, I expect more users not to be acquainted with this sort of concept. And it's pretty important here, not to have an expensive function being called too many times.

Also wondering if this API could in the future be adapted to the other interactive plotting panes, like Bokeh/Matplotlib...

[MarcSkovMadsen]

+1 for a Commons event API, especially Across plot panes.