Expose all supported GHC versions (copy #2987)

[mergify]

Right now the only default GHC version gets exported by the flake. This means that libraries wanting to use the clash-compiler flake realistically can only support the default GHC version. If someone wants to use any of the other supported versions, that would work fine for clash-compiler, but it wouldn't trickle down to the libraries (which are stuck with the default ghc version).

Graphs visualizing the issue:
If you want to develop with the default version (ghc9101)

myprogram => ghc9101
 |- clash-compiler => ghc9101
 \- clash-protocols => ghc9101
     |- clash-compiler => ghc9101
     \- circuit-notation => ghc9101
         \- clash-compiler => ghc9101

With a non-default, but supported version (ghc964)

myprogram => ghc964
 |- clash-compiler => ghc964
 \- clash-protocols => ghc9101
     |- clash-compiler => ghc9101
     \- circuit-notation => ghc9101
         \- clash-compiler => ghc9101

By exposing all supported libraries, clash-* libraries can be adapted to build for the same set of ghc versions.

Still TODO:

• Write a changelog entry (see changelog/README.md)
• Check copyright notices are up to date in edited files

---

This is an automatic copy of pull request #2987 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 6a08104 has failed:

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	both modified:   flake.nix

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