Capture stdout and stderr in pyodide execution

[philippjfr]

Cleans up utilities for rendering output in Pyodide.

[codecov]

Codecov Report

Merging #3856 (f59ee1b) into master (be08046) will decrease coverage by 48.64%.
The diff coverage is 12.50%.

@@             Coverage Diff             @@
##           master    #3856       +/-   ##
===========================================
- Coverage   83.01%   34.36%   -48.65%     
===========================================
  Files         224      224               
  Lines       32699    32701        +2     
===========================================
- Hits        27146    11239    -15907     
- Misses       5553    21462    +15909     

Flag	Coverage Δ
ui-tests	34.36% <12.50%> (-0.06%)	⬇️
unitexamples-tests	?

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Impacted Files	Coverage Δ
panel/io/pyodide.py	0.00% <0.00%> (ø)
panel/tests/io/test_mime_render.py	50.00% <20.00%> (-50.00%)	⬇️
panel/io/mime_render.py	24.21% <21.73%> (-64.57%)	⬇️
panel/__main__.py	0.00% <0.00%> (-100.00%)	⬇️
panel/models/katex.py	0.00% <0.00%> (-100.00%)	⬇️
panel/models/mathjax.py	0.00% <0.00%> (-100.00%)	⬇️
panel/models/perspective.py	0.00% <0.00%> (-100.00%)	⬇️
panel/pane/vtk/synchronizable_deserializer.py	0.00% <0.00%> (-97.59%)	⬇️
panel/models/ace.py	0.00% <0.00%> (-91.67%)	⬇️
panel/tests/widgets/test_input.py	8.86% <0.00%> (-91.14%)	⬇️
... and 158 more

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