CLN: Fix typos (mainly in docs and comments)

[minho42]

• closes #xxxx
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[topper-123]

Very nice patch! It needs a rebase, so ping when green.

[TomAugspurger]

FYI, it may be easier to split this into smaller pieces, to avoid merge conflicts like the one that came up.

[datapythonista]

Great job @minho42, nice clean up.

Let us know if you need help resolving the conflicts.

[minho42]

I tried to rebase, but not sure if it's okay.
Please change/amend further if necessary.

[datapythonista]

Looks ok, let's wait until the CI finishes, but this should be ready to be merged. Thanks @minho42

[codecov]

Codecov Report

Merging #27007 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #27007      +/-   ##
==========================================
- Coverage   91.99%   91.99%   -0.01%     
==========================================
  Files         180      180              
  Lines       50774    50774              
==========================================
- Hits        46711    46708       -3     
- Misses       4063     4066       +3

Flag	Coverage Δ
#multiple	90.63% <100%> (ø)	⬆️
#single	41.85% <0%> (-0.07%)	⬇️

Impacted Files	Coverage Δ
pandas/io/json/normalize.py	96.93% <ø> (ø)	⬆️
pandas/core/arrays/period.py	98.54% <ø> (ø)	⬆️
pandas/plotting/_matplotlib/tools.py	78.53% <ø> (ø)	⬆️
pandas/core/dtypes/common.py	96.35% <ø> (ø)	⬆️
pandas/util/testing.py	90.94% <ø> (+0.1%)	⬆️
pandas/core/indexes/interval.py	96.44% <ø> (ø)	⬆️
pandas/core/resample.py	97.23% <ø> (ø)	⬆️
pandas/tseries/offsets.py	96.36% <ø> (ø)	⬆️
pandas/core/indexes/datetimes.py	96.37% <ø> (ø)	⬆️
pandas/core/indexes/base.py	96.92% <ø> (ø)	⬆️
... and 30 more

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[datapythonista]

Thanks @minho42