Reduce 2.12 / 2.13 Jar size by using instance constructors

[joroKr21]

Generate less anonymous classes for implicit instances,
esp. for tuple and function instances which are code generated.

Note: this slightly increases the Jar size on 2.11 because it doesn't translate to LambdaMetaFactory

[milessabin]

Retrospectively ... LGTM!

[catostrophe]

@joroKr21 this probably breaks bincompat on 2.12 only

Moving Aux from the *Instances trait to the object led to:

[error] Symbol 'type shapeless.ops.FnFromProductInstances.Aux' is missing from the classpath.
[error] This symbol is required by 'value io.circe.generic.decoding.IncompleteDerivedDecoders.ffp'.

[joroKr21]

@catostrophe that is surprising to me - I thought type aliases are erased and moving them around doesn't break binary compatibility. Also MiMa didn't complain. So maybe something more going on. Will have to investigate ...

[catostrophe]

@joroKr21 It works on 2.13.5, but fails on 2.12.13
I hope the provided details are sufficient to reproduce the issue

[joroKr21]

I opened lightbend-labs/mima#627
The fix is obvious - we will have to move the type aliases back to the traits

[catostrophe]

Oh no. The whole circe family has been released with shapeless 2.3.6. It just breaks in compiletime with 2.3.7.

[catostrophe]

@joroKr21 could you add a comment to 2.3.6 release notes that it shouldn't be used?