Add alias-demut pass

[nomeata]

This pass lifts type aliases out of recursive groups. There is only one such alias (resulttype), but who knows what comes up later.

It fails ungracefully (relying on the il validator) if the aliases are themselves recursive.

This simplifies generation of Rocq or Lean.

[nomeata]

Hmm, CI on github fails with

Fatal error: exception Stack overflow

but it works fine locally here.

[DCupello1]

Looks good!

About the stack overflow, I have the same issue when trying to merge the uncase removal pass to main #191 .

@rossberg: these two passes do completely different things, so its very likely to be a CI issue. What can we do about this?

[rossberg]

Did you try a make clean before running the tests locally? If yes, then I don't know what the cause is or what we can do about it. Perhaps the CI environment is configured to use smaller stack space by default?

[nomeata]

It might be that mdx_gen.bc.exe itself is stack overflowing, given the huge TEST.md file. That’s consistent with Diegos PR also failing as he adds yet another pass.

So maybe #194 (which I’d advocate for nevertheless) will just avoid this problem, but not using mdx and using pure dune for running tests.

[nomeata]

Indeed #194 helps

[DCupello1]

Great! I'll do the same with #191