Add `Require Extraction` to Coq output
The .v file generated by Menhir contains Extract
directives, which are no longer accepted if the Extraction
standard library module has not been loaded before. Currently, there's an indirect dependency MenhirLib -> FSetAVL -> MSetAVL -> FunInd -> Extraction, but this is about to change, so better be explicit.
Refs: https://github.com/AbsInt/CompCert/pull/515 https://github.com/coq/coq/pull/19343