Revert "DOC: Remove vendored IPython.sphinext (#18193)"

[jorisvandenbossche]

This reverts commit ca737ac.

This reverts #18193. The problem is there is something wrong with the upstream version such that errors in the code don't get reported.

[codecov]

Codecov Report

Merging #18320 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #18320      +/-   ##
==========================================
- Coverage   91.39%   91.37%   -0.02%     
==========================================
  Files         164      164              
  Lines       49808    49808              
==========================================
- Hits        45520    45511       -9     
- Misses       4288     4297       +9

Flag	Coverage Δ
#multiple	89.17% <ø> (ø)	⬆️
#single	39.47% <ø> (-0.07%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.8% <0%> (-0.1%)	⬇️

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[jorisvandenbossche]

@TomAugspurger I identified the source of the problem: ipython/ipython#9823 So another option is to pin IPython to an older version (although I would maybe rather vendor the latest upstream version + bug fix, to mimic that we are using the latest IPython version)

[jorisvandenbossche]

I opened an issue at IPython: ipython/ipython#10904 (with potential solution)

[TomAugspurger]

Thanks for tracking it down @jorisvandenbossche. I think reverting ca737ac for now is fine. And then once the next IPython is released with your fix, we'd require it for building the docs.