Expose a public property to sort extensions deterministically.

[Zsailer]

This provides a single, public property in the server extension API to return a deterministic list of server extensions.

This doesn't change much in server. We were already sorting extensions alphabetically by their keys. This change allows nbclassic to monkey-patch this property (as a special case) and provide a list of server extensions with nbclassic always first and the rest sorted alphabetically. See jupyter/nbclassic#56 for more details.

[codecov-commenter]

Codecov Report

Merging #522 (830e006) into master (6bf5914) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #522      +/-   ##
==========================================
- Coverage   76.99%   76.98%   -0.01%     
==========================================
  Files         107      107              
  Lines        9511     9499      -12     
  Branches     1032     1031       -1     
==========================================
- Hits         7323     7313      -10     
+ Misses       1815     1814       -1     
+ Partials      373      372       -1     

Impacted Files	Coverage Δ
jupyter_server/services/config/manager.py	100.00% <ø> (ø)
jupyter_server/extension/manager.py	88.70% <100.00%> (+0.18%)	⬆️
jupyter_server/services/nbconvert/handlers.py	80.95% <0.00%> (-2.39%)	⬇️
...upyter_server/services/contents/filecheckpoints.py	62.94% <0.00%> (-0.65%)	⬇️
...pyter_server/services/contents/largefilemanager.py	82.41% <0.00%> (-0.57%)	⬇️
jupyter_server/services/contents/fileio.py	75.26% <0.00%> (-0.39%)	⬇️
jupyter_server/services/contents/filemanager.py	66.31% <0.00%> (-0.22%)	⬇️
jupyter_server/tests/extension/test_manager.py	100.00% <0.00%> (ø)
jupyter_server/tests/test_terminal.py	98.80% <0.00%> (+2.33%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 284c938...830e006. Read the comment docs.

[blink1073]

Thanks! Test failure looks to be related to a recent upstream release