Make the vals inside all 'Ops' style classes private

[coltfred]

This PR is to make private all the values inside the Ops style classes. This came from #2613.

TODO

• Add examples which show all the syntax still works.

[codecov-io]

Codecov Report

Merging #2617 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #2617      +/-   ##
==========================================
- Coverage   95.17%   95.14%   -0.03%     
==========================================
  Files         363      363              
  Lines        6693     6695       +2     
  Branches      307      291      -16     
==========================================
  Hits         6370     6370              
- Misses        323      325       +2

Impacted Files	Coverage Δ
core/src/main/scala/cats/data/Validated.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/ApplicativeError.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/syntax/monoid.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/syntax/applicative.scala	100% <ø> (ø)	⬆️
free/src/main/scala/cats/free/FreeT.scala	90.66% <ø> (ø)	⬆️
core/src/main/scala/cats/data/Const.scala	100% <ø> (ø)	⬆️
...src/main/scala/cats/syntax/unorderedFoldable.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/syntax/apply.scala	25% <ø> (ø)	⬆️
core/src/main/scala/cats/syntax/set.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/syntax/either.scala	99.26% <ø> (ø)	⬆️
... and 26 more

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[kailuowang]

Thanks so much!

[kailuowang]

Thanks so much!