Add ADVal instances that correspond to what package `ad` has

[Mikolaj]

Add ADVal instances that correspond to AD instances in package ad (https://hackage.haskell.org/package/ad-4.5.6/docs/Numeric-AD.html#t:AD) or document why it's not possible. An example of such an instance is https://hackage.haskell.org/package/erf-2.0.0.0/docs/Data-Number-Erf.html#t:Erf.

If anything else obviously should be added, e.g., from packages that depend on ad, then let's do it as well.

Edit: and for the symbolic pipelines to work, the same instances need to be defined for the AstTensor type.