Handle Django compatibility

[philippjfr]

Improve dispatching to DjangoConsumer in panel.io.document.unlocked contextmanager and add forward compatibility for bokeh_django.

@sdc50 Please test.

[codecov]

Codecov Report

Merging #3835 (a0ef99e) into master (3a7a791) will decrease coverage by 0.09%.
The diff coverage is 24.00%.

@@            Coverage Diff             @@
##           master    #3835      +/-   ##
==========================================
- Coverage   82.89%   82.80%   -0.10%     
==========================================
  Files         222      222              
  Lines       32395    32411      +16     
==========================================
- Hits        26853    26837      -16     
- Misses       5542     5574      +32     

Flag	Coverage Δ
ui-tests	33.88% <8.00%> (-0.34%)	⬇️
unitexamples-tests	75.24% <24.00%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
panel/io/document.py	61.76% <9.52%> (-4.91%)	⬇️
panel/io/django.py	30.76% <100.00%> (+4.23%)	⬆️
panel/tests/ui/io/test_jupyter_server_extension.py	40.74% <0.00%> (-59.26%)	⬇️
panel/tests/conftest.py	86.78% <0.00%> (-1.33%)	⬇️
panel/util.py	86.41% <0.00%> (-0.76%)	⬇️

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[sdc50]

@philippjfr Sorry I didn't see this yesterday. I just tested and it works great!

I'm still working through what needs to be fixed when setting BOKEH_RESOURCES to server. From what I can tell so far it seems to be a limitation with bokeh.embed.bundle.bundle_for_objs_and_resources not allowing you to specify a root_url.