Add adaptErr to ApplicativeErrorOps

[bplommer]

Partially addresses #2685.

I've changed MonadError#adaptError to be an alias for ApplicativeErrorOps#adaptErr, but I wasn't sure whether I should do this or provide a duplicate implementation.

[codecov-io]

Codecov Report

Merging #2698 into master will decrease coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2698      +/-   ##
==========================================
- Coverage   95.16%   95.12%   -0.04%     
==========================================
  Files         365      365              
  Lines        6777     6796      +19     
  Branches      302      293       -9     
==========================================
+ Hits         6449     6465      +16     
- Misses        328      331       +3

Impacted Files	Coverage Δ
.../src/main/scala/cats/syntax/applicativeError.scala	100% <100%> (ø)	⬆️
core/src/main/scala/cats/MonadError.scala	100% <100%> (ø)	⬆️
core/src/main/scala/cats/syntax/foldable.scala	100% <0%> (ø)	⬆️
...patTest/src/main/scala/catsBC/MimaExceptions.scala	0% <0%> (ø)	⬆️
core/src/main/scala/cats/data/Kleisli.scala	97.29% <0%> (+0.02%)	⬆️

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[kailuowang]

thanks so much for taking on this! Here is some feedback

1. I would duplicate the code with the same comment you have on syntax.
2. I would leave the laws unchanged and leave that to the future PR that moves the method to the ApplicativeError. The change breaks binary compatibility in cats-laws (which we don't check at the moment), and conventionally everything in XXXXlaws should be in XXXXTests, which we can't do since it's in the syntax ops. Instead, we can add a doctest to the syntax method in ApplicativeErrorOps

[kailuowang]

Thanks @bplommer

[LukaJCB]

Looks great, thanks @bplommer! 😊