[GHC 9.2] Deprecate SimpleGetter and SimpleFold, make 8.6 the lowest supported version, do a major version bump

[neongreen]

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[neongreen]

Ok, everything is worse than I thought it is.

People normally often don't put an upper bound on microlens (http://packdeps.haskellers.com/reverse/microlens), i.e. if microlens gains a contravariant dependency it means a lot of people will have a sudden contravariant dependency on their hands. It's not that terrible because they will only get a dependency if they are using old GHCs. Still, not great. A major version bump doesn't help at all here.

On the other hand, if I carry on with SimpleGetter forever, it will always be a slightly confusing wart. Conditionally exporting Getter, producing it, etc, is better because most people won't be stuck with the wart, but conditional exports are more confusing and potentially annoying to debug, so I don't like this option either.

Retroactively removing GHC >8.6 support from old microlens versions is not an option because revisions break Nix.

Meh.

[neongreen]

Ok, I made a decision. microlens will focus on being minimal, and SimpleGetter will remain a confusing wart. There will be no conditional export of Getter.microlens-th will continue producing SimpleGetter and SimpleFold.

One day I will make GHC 8.6 the lowest supported version, and then SimpleGetter and friends will go away.