Allow invoking convert from pyodide

[philippjfr]

Fixes #4067

[codecov]

Codecov Report

Merging #4135 (e8c513d) into master (ebd7fc5) will increase coverage by 0.02%.
The diff coverage is 90.00%.

@@            Coverage Diff             @@
##           master    #4135      +/-   ##
==========================================
+ Coverage   83.56%   83.58%   +0.02%     
==========================================
  Files         224      224              
  Lines       33381    33391      +10     
==========================================
+ Hits        27895    27911      +16     
+ Misses       5486     5480       -6     

Flag	Coverage Δ
ui-tests	37.64% <90.00%> (+0.01%)	⬆️
unitexamples-tests	74.56% <13.33%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
panel/io/convert.py	72.13% <90.00%> (-0.10%)	⬇️
panel/pane/base.py	88.75% <0.00%> (+0.83%)	⬆️
panel/tests/util.py	89.32% <0.00%> (+0.97%)	⬆️
panel/tests/pane/test_base.py	96.00% <0.00%> (+12.00%)	⬆️

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