Restruct functor

[kailuowang]

Big but rather mechanical changes according to #1930

1. Move Profunctor and Strong to the arrow package
2. Move Bifunctor, Invariant and Contravariant to root package

[codecov-io]

Codecov Report

Merging #1934 into master will increase coverage by 0.02%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master    #1934      +/-   ##
==========================================
+ Coverage   95.55%   95.57%   +0.02%     
==========================================
  Files         248      248              
  Lines        4430     4454      +24     
  Branches      116      110       -6     
==========================================
+ Hits         4233     4257      +24     
  Misses        197      197

Impacted Files	Coverage Δ
laws/src/main/scala/cats/laws/BifunctorLaws.scala	100% <ø> (ø)	⬆️
...in/scala/cats/laws/discipline/CartesianTests.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/arrow/Profunctor.scala	100% <ø> (ø)
core/src/main/scala/cats/data/Validated.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/data/Func.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/Bitraverse.scala	80% <ø> (ø)	⬆️
core/src/main/scala/cats/data/Nested.scala	100% <ø> (ø)	⬆️
...e/src/main/scala/cats/ContravariantCartesian.scala	66.66% <ø> (ø)	⬆️
core/src/main/scala/cats/instances/function.scala	100% <ø> (ø)	⬆️
...in/scala/cats/laws/discipline/BifunctorTests.scala	100% <ø> (ø)	⬆️
... and 35 more

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[edmundnoble]

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[tpolecat]

👍