fixed-point argument parameter on derivations

[RossSmyth]

Is your feature request related to a problem? Please describe.
Would be nice if the derivations here supported fixed-point arguments, i.e. finalAttrs.

Describe the solution you'd like

This would require reworking the derivations to use lib.extendMkDerivation ideally. I played around with this and there is one main blocker: the stdenv attribute.

Describe alternatives you've considered
Could roll our own helper, but it is nice to be in-sync with any update to extendMkDerivation.

Additional context
Add any other context or screenshots about the feature request here.

[ipetkov]

I've never used lib.extendMkDerivation what are the upsides and where is it useful here?