Add support for rendering in pyodide/pyscript

[philippjfr]

Implements a pyodide_extension that registers MIME rendering hooks that work in pyodide/pyscript.

[codecov-commenter]

Codecov Report

Merging #5338 (e3067e2) into master (d4a2de2) will decrease coverage by 0.00%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master    #5338      +/-   ##
==========================================
- Coverage   88.16%   88.16%   -0.01%     
==========================================
  Files         300      300              
  Lines       61912    61915       +3     
==========================================
+ Hits        54585    54587       +2     
- Misses       7327     7328       +1     

Impacted Files	Coverage Δ
holoviews/__init__.py	72.22% <66.66%> (-0.86%)	⬇️
holoviews/util/__init__.py	75.51% <100.00%> (+0.04%)	⬆️

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[MarcSkovMadsen]

Will this enable streaming to plots or from plots? I.e. dynamically updating the plot data or getting hover/ selection etc. events.

[philippjfr]

Will this enable streaming to plots or from plots? I.e. dynamically updating the plot data or getting hover/ selection etc. events.

This is already possible with master if you render plots manually using the pn.io.pyodide.write or .servable(target=...) API. This PR simply allows the pyscript repr system to work on HoloViews objects.