Add explicit type annotations for implicit Ordering vals

[travisbrown]

Dotty was complaining about some of these, so I went ahead and took care of all the Ordering ones.

Now the only implicit vals in core without type annotations are things like new OptionTMonad[F] { implicit val F = F0 }, which Dotty is fine with. There are still a lot of others in cats-tests, which I'm not able to compile on Dotty yet because I don't have the laws modules working.

The cases in this PR are all local definitions and they're a little more verbose, but personally seeing implicit val whatever = makes me anxious even in this context, and I think it's worth making this change even apart from the Dotty considerations.

[codecov-io]

Codecov Report

Merging #3188 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #3188   +/-   ##
=======================================
  Coverage   92.99%   92.99%           
=======================================
  Files         376      376           
  Lines        7381     7381           
  Branches      195      195           
=======================================
  Hits         6864     6864           
  Misses        517      517

Flag	Coverage Δ
#scala_version_212	93.32% <100%> (ø)	⬆️
#scala_version_213	90.58% <81.25%> (-0.02%)	⬇️

Impacted Files	Coverage Δ
core/src/main/scala/cats/data/NonEmptyList.scala	98.7% <100%> (ø)	⬆️
core/src/main/scala/cats/syntax/set.scala	100% <100%> (ø)	⬆️
core/src/main/scala/cats/instances/sortedSet.scala	85.71% <100%> (ø)	⬆️
core/src/main/scala/cats/data/Chain.scala	98.43% <100%> (ø)	⬆️
.../main/scala-2.13+/cats/data/NonEmptyLazyList.scala	62.5% <100%> (ø)	⬆️
...rc/main/scala/cats/laws/discipline/arbitrary.scala	99.14% <100%> (ø)	⬆️
core/src/main/scala/cats/data/NonEmptyVector.scala	99.15% <100%> (ø)	⬆️
core/src/main/scala/cats/data/NonEmptySet.scala	97.64% <100%> (ø)	⬆️
core/src/main/scala/cats/syntax/list.scala	100% <100%> (ø)	⬆️

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