Separate Plated into own package

[phadej]

• Plated class isn't lens specific.
• optics (and other lens libraries, e.g. microlens users) would benefit from having just one Plated
• this would allow to inverse dependency so lens-aeson wouldn't need to have orphan Plated, but it could be provided by aeson `itself.
  • this could be done at the same time when lens-aeson & aeson-optics drop support for aeson<2 (soon, but not too soon).
• This is similar to splitting out indexed traversables

[mikeplus64]

Any word on this?