Make the value of the class private

[coltfred]

This makes the .value of two of the Ops classes private, since they shouldn't ever be referenced and they collide with Scalatest.

Fixes #2514 and #2613

[codecov-io]

Codecov Report

Merging #2614 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #2614      +/-   ##
==========================================
- Coverage   95.17%   95.15%   -0.03%     
==========================================
  Files         361      361              
  Lines        6658     6660       +2     
  Branches      303      303              
==========================================
  Hits         6337     6337              
- Misses        321      323       +2

Impacted Files	Coverage Δ
core/src/main/scala/cats/syntax/nested.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/syntax/either.scala	99.26% <ø> (ø)	⬆️
...patTest/src/main/scala/catsBC/MimaExceptions.scala	0% <0%> (ø)	⬆️

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[kailuowang]

Thanks! Would you also add usages of the syntax to https://github.com/typelevel/cats/blob/master/binCompatTest/src/main/scala/catsBC/MimaExceptions.scala
something like
"blah".leftNec[Int]

This will make sure that such usages are still binary compatible.

[kailuowang]

once this approach is approved, I'd like to update all value classes fields to private in Cats

[coltfred]

@kailuowang Added.

[coltfred]

I think I've proven to myself that things still work as expected, so this should be ready for actual review.

[kailuowang]

Thanks @coltfred

[kailuowang]

@rossabaker @ceedubs @LukaJCB what do you think of this?
This is mostly to fix to the public field of value classes causing conflicts with other extensions. We had to make them public due to restrictions on scala 2.10 but we already dropped 2.10 support. If you all agree with this approach, I am going to create an issue to make all* value class fields private.

[LukaJCB]

This looks very reasonable, If everything still works as is then I'm happy to change this for all the extensions. Are we going to do an 1.5.0-RC1? We could make sure everything still works with that release :)

[kailuowang]

@LukaJCB yes I think we should do a RC1

[coltfred]

I'm more than happy to give a 1.5.0-RC1 a try today or this weekend.

[rossabaker]

All binary exceptions make me nervous, but I think this one is justified. External calls to .value would be silly, and the classes are final so nobody downstream is making a BiggerAndBetterOps class that needs it.