3.8.0~alpha3

CHANGES:

• merlin: ignore instrumentation settings for preprocessing. (#7606, fixes
  #7465, @Alizter)

• Add a coqdoc_flags field to the coq.theory stanza allowing the user to
  pass extra arguments to coqdoc. (#7676, fixes #7954 @Alizter)

• Coq language versions less 0.8 are deprecated, and will be removed
  in an upcoming Dune version. All users are required to migrate to
  (coq lang 0.8) which provides the right semantics for theories
  that have been globally installed, such as those coming from opam
  (@ejgallego, @Alizter)

• Bump minimum version of the dune language for the melange syntax extension
  from 3.7 to 3.8 (#7665, @jchavarri)