NDFrame.filter -> NDFrame.select

[topper-123]

• closes Rename NDFrame.filter to .select? #26642
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

This PR moves NDFrame.filter over to NDFrame.select and deprecates NDFrame.filter.

I'm not completely happy with the siganture from .filter, and got some discussion points in #26642. The current PR can be seen as a first version, to be changed, if there's agreement,

[codecov]

Codecov Report

Merging #26866 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #26866      +/-   ##
==========================================
- Coverage   91.88%   91.87%   -0.01%     
==========================================
  Files         179      179              
  Lines       50696    50700       +4     
==========================================
- Hits        46581    46580       -1     
- Misses       4115     4120       +5

Flag	Coverage Δ
#multiple	90.46% <100%> (ø)	⬆️
#single	41.09% <14.28%> (-0.08%)	⬇️

Impacted Files	Coverage Δ
pandas/core/generic.py	94.2% <100%> (+0.01%)	⬆️
pandas/io/gbq.py	88.88% <0%> (-11.12%)	⬇️
pandas/core/frame.py	96.88% <0%> (-0.12%)	⬇️
pandas/util/testing.py	90.84% <0%> (-0.11%)	⬇️

---

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[codecov]

Codecov Report

Merging #26866 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #26866      +/-   ##
==========================================
- Coverage   91.88%   91.87%   -0.01%     
==========================================
  Files         179      179              
  Lines       50696    50700       +4     
==========================================
  Hits        46581    46581              
- Misses       4115     4119       +4

Flag	Coverage Δ
#multiple	90.46% <100%> (ø)	⬆️
#single	41.11% <14.28%> (-0.06%)	⬇️

Impacted Files	Coverage Δ
pandas/core/generic.py	94.2% <100%> (+0.01%)	⬆️
pandas/io/gbq.py	88.88% <0%> (-11.12%)	⬇️
pandas/core/frame.py	96.88% <0%> (-0.12%)	⬇️

---

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 430f0fd...69c37a7. Read the comment docs.

[jreback]

we should have a discussion about these semantics in the issue, can you summarize there

[TomAugspurger]

We need to have at least one release without NDFrame.select, before we can change it to be the new name for filter, right?

[topper-123]

I've set up an issue at #26642.

[topper-123]

I'm closing this donw temporarily. As I'vr said in #26642, I'm in favor ofmaking a specialized method that wouldn't overlap too much .loc.