Handle cyclic module dependencies

[maximebuyse]

Closes #396

The idea is to put together objects that create a cyclic dependency at the module level. We bundle them in a newly created module (one for each cycle) and then use FStarLang/FStar#3369 to selectively include these objects in the module they actually belong to.
List of changes compared to the existing implementation (that was present in dependencies.ml but not used by any backend):

• we solve name clashes in the bundles (by adding a hash to the names that clash)
• we replace the let and type keywords by and for mutually recursive items
• we replace the unfold let by include to make use of Add a new syntax to support partial opens and includes FStarLang/FStar#3369
• we bundle not only mutually recursive items but also items that create a cyclic dependency without being recursive. This is done by computing the transitive closure of the item dependency graph. Looking for paths of three objects a1 -> b -> a2 such that a1, a2 belong to module A and b belongs to B (with B != A). Adding an edge between these items for each such path in a new graph. After finding all such paths, the bundles are exactly the connected components of this new graph.

[W95Psp]

As we discussed, we should rename constructors in enumeration when their name are clashing, see https://hax-playground.cryspen.com/#fstar/0559a9e0ba/gist=02128b3051501d2c361787c887a82d26

[maximebuyse]

As we discussed, we should rename constructors in enumeration when their name are clashing, see https://hax-playground.cryspen.com/#fstar/0559a9e0ba/gist=02128b3051501d2c361787c887a82d26

As discussed, it is easier (and maybe better as we keep the naming convention) to always rename the variants when we rename the enum. We also need to include the new variants in the module of origin with an alias (to make sure the original name is available).

I implemented that. Note that the import of variants also happens when there is no renaming (not sure if it is good or not).

[W95Psp]

Thanks, that's great!
Let's merge it! 😃