Move Unchanged arith methods to EA mixins

[jbrockmendel]

Next steps after #19902. Breaking these up into smaller pieces than usual because I don't know what bits will prove controversial.

All this PR does is take a few of the easiest no-changes-needed methods and moved them to the EA mixins.

[codecov]

Codecov Report

Merging #21712 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #21712      +/-   ##
==========================================
+ Coverage    91.9%   91.91%   +<.01%     
==========================================
  Files         158      158              
  Lines       49690    49689       -1     
==========================================
+ Hits        45670    45671       +1     
+ Misses       4020     4018       -2

Flag	Coverage Δ
#multiple	90.28% <100%> (ø)	⬆️
#single	41.95% <43.75%> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/core/indexes/period.py	92.55% <ø> (-0.04%)	⬇️
pandas/core/indexes/datetimelike.py	96.87% <ø> (+0.15%)	⬆️
pandas/core/indexes/timedeltas.py	91.08% <ø> (-0.11%)	⬇️
pandas/core/arrays/datetimelike.py	94.52% <100%> (+1.76%)	⬆️
pandas/core/arrays/period.py	100% <100%> (ø)	⬆️
pandas/core/arrays/timedelta.py	100% <100%> (ø)	⬆️

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[jreback]

lgtm. @TomAugspurger @jorisvandenbossche if any comments.

[jreback]

thanks @jbrockmendel