F* built with dune : new library layout

[tahina-pro]

Dear all,

I will be merging #2815 soon, some time this week. That PR will build F* with dune instead of ocamlbuild.
In this process, the following changes will mostly impact F* users who compile OCaml code extracted from F* programs:

• fstar-lib, fstar-tactics-lib and fstar-compiler-lib will be merged into a single library, fstar.lib
• If you use F* from its source repository, fstar.lib will be located in $FSTAR_HOME/lib/fstar/lib/fstar_lib.cmx* instead of $FSTAR_HOME/bin/*.cmx*, so that you should update your OCAMLPATH to $FSTAR_HOME/lib instead of $FSTAR_HOME/bin. (If you install F* via opam, you shouldn't need to update OCAMLPATH.)
• The F* tactic library will be statically linked with the F* compiler.
• In the F* binary package, the F* standard library will be in lib/fstar instead of ulib .

Please test the PR with your installations.

Thank you in advance!

[tahina-pro]

@paracetamolo How does this PR impact your ongoing work on improving integration of libraries developed in F* into OCaml projects? Thanks in advance for your feedback!