Improve detection of comms in vscode and colab

[hoxbro]

Fixes #3767

Before this PR if hv.extension was called before pn.extension it will be set pn.config.comms to "default" and not vscode in vs code or colab in Google Colab.

This PR refactors the detection into its own method and always calls in a notebook. On the first run, it will auto-detect the comms and replace None with one of default, ipywidgets, vscode, or colab. Then in the following calls, it will only change the comms if it is explicitly set.

I'm unsure if the order of pyodide and vscode should be swapped.

[codecov]

Codecov Report

Merging #4115 (8c452c1) into master (6d90165) will decrease coverage by 0.00%.
The diff coverage is 8.33%.

@@            Coverage Diff             @@
##           master    #4115      +/-   ##
==========================================
- Coverage   83.58%   83.58%   -0.01%     
==========================================
  Files         223      223              
  Lines       33248    33244       -4     
==========================================
- Hits        27792    27788       -4     
  Misses       5456     5456              

Flag	Coverage Δ
ui-tests	37.56% <8.33%> (-0.01%)	⬇️
unitexamples-tests	74.66% <8.33%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
panel/config.py	74.93% <8.33%> (-1.34%)	⬇️
panel/tests/command/test_serve.py	83.95% <0.00%> (-1.42%)	⬇️
panel/tests/util.py	91.17% <0.00%> (-0.09%)	⬇️
panel/io/jupyter_server_extension.py	0.00% <0.00%> (ø)
panel/io/state.py	69.83% <0.00%> (+0.01%)	⬆️
panel/tests/ui/widgets/test_tabulator.py	99.07% <0.00%> (+0.10%)	⬆️
panel/pane/idom.py	28.36% <0.00%> (+0.19%)	⬆️
panel/tests/conftest.py	88.79% <0.00%> (+0.38%)	⬆️
panel/io/callbacks.py	79.41% <0.00%> (+0.57%)	⬆️
panel/command/convert.py	32.35% <0.00%> (+0.92%)	⬆️

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[philippjfr]

Looks good to me. Ready to merge?

[hoxbro]

Yes