Add TypeVar to deprecate_kwarg_name to preserve type information

[nint8835]

Fixes issue initially reported in #1308, based off changes in #1348.

Initially reported issue reported issues with functions typed with deprecate_kwarg_name, but the fix PR fixed deprecate_kwarg which appeared to suffer from the same issue. I'm encountering the initially reported issue with calls to .text still, so this PR applies the fix from the initial issue description to the deprecate_kwarg_name class as well.

I've tested locally and confirmed this resolves typing issues on .text for me.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.33%. Comparing base (6b3b14a) to head (59fb8bc).
Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1733   +/-   ##
=======================================
  Coverage   95.32%   95.33%           
=======================================
  Files          27       28    +1     
  Lines        6788     6842   +54     
  Branches     1013     1025   +12     
=======================================
+ Hits         6471     6523   +52     
- Misses        193      194    +1     
- Partials      124      125    +1     

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[adam-urbanczyk]

Simple change, merging. Thanks @nint8835 !