Add --attribute-comment argument to JS and TSD clients

[sderickson]

Add --attribute-comment field to js_client.py and tsd_client.py, like the one added to python_client.py in #262. This is a prerequisite for dropbox/dropbox-sdk-js#891 which adds scopes to the outputted clients for easier reference.

Also adds appropriate testing and updates the docstring for the python_client.py, making it more succinct and aligned with the other two.

Checklist

General Contributing

• Have you read the Code of Conduct and signed the CLA?

Is This a Code Change?

• Non-code related change (markdown/git settings etc)
• Code Change
• Example/Test Code Change

Validation

• Have you ran tox?
• Do the tests pass?

[codecov]

Codecov Report

Merging #268 (56a635d) into main (90dd831) will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #268      +/-   ##
==========================================
+ Coverage   51.90%   52.02%   +0.11%     
==========================================
  Files          37       37              
  Lines        8437     8458      +21     
  Branches     1800     1810      +10     
==========================================
+ Hits         4379     4400      +21     
  Misses       3741     3741              
  Partials      317      317              

Flag	Coverage Δ
unit	52.02% <100.00%> (+0.11%)	⬆️

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

Impacted Files	Coverage Δ
stone/backends/python_client.py	46.66% <ø> (ø)
stone/backends/js_client.py	80.72% <100.00%> (+2.64%)	⬆️
stone/backends/tsd_client.py	60.00% <100.00%> (+4.68%)	⬆️

---

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 90dd831...56a635d. Read the comment docs.