DEPR: deprecate pd.TimeGrouper

[jreback]

closes #16747

[codecov]

Codecov Report

Merging #17703 into master will decrease coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #17703      +/-   ##
==========================================
- Coverage   91.27%   91.22%   -0.05%     
==========================================
  Files         163      163              
  Lines       49760    49765       +5     
==========================================
- Hits        45416    45400      -16     
- Misses       4344     4365      +21

Flag	Coverage Δ
#multiple	89.02% <100%> (-0.03%)	⬇️
#single	40.34% <25%> (-0.07%)	⬇️

Impacted Files	Coverage Δ
pandas/core/api.py	100% <100%> (ø)	⬆️
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/plotting/_converter.py	63.38% <0%> (-1.82%)	⬇️
pandas/core/frame.py	97.73% <0%> (-0.1%)	⬇️

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