Undeprecate ReactTemplate and deprecate Viewable.pprint

[philippjfr]

I'm not yet sure about template deprecations so I'm leaving it, but Viewable.pprint is superfluous and is now to be removed.

[codecov]

Codecov Report

Merging #4347 (940ca1a) into main (bcfbcba) will decrease coverage by 9.07%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #4347      +/-   ##
==========================================
- Coverage   82.78%   73.71%   -9.07%     
==========================================
  Files         240      240              
  Lines       34632    34631       -1     
==========================================
- Hits        28670    25529    -3141     
- Misses       5962     9102    +3140     

Flag	Coverage Δ
ui-tests	?
unitexamples-tests	73.71% <0.00%> (-0.04%)	⬇️

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Impacted Files	Coverage Δ
panel/template/react/__init__.py	100.00% <ø> (ø)
panel/viewable.py	65.74% <0.00%> (-0.21%)	⬇️
panel/tests/ui/widgets/test_tabulator.py	9.50% <0.00%> (-89.61%)	⬇️
panel/tests/ui/widgets/test_input.py	11.34% <0.00%> (-88.13%)	⬇️
panel/tests/ui/layout/test_accordion.py	14.72% <0.00%> (-85.28%)	⬇️
panel/tests/ui/widgets/test_sliders.py	15.42% <0.00%> (-84.58%)	⬇️
panel/tests/ui/layout/test_card.py	18.01% <0.00%> (-81.99%)	⬇️
panel/tests/ui/io/test_convert.py	15.51% <0.00%> (-80.18%)	⬇️
panel/tests/ui/widgets/test_image.py	25.80% <0.00%> (-74.20%)	⬇️
panel/tests/ui/test_reactive.py	26.53% <0.00%> (-73.47%)	⬇️
... and 36 more

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