[rocq] Changes entry

Author: ejgallego

doc/changes/added/12035.md

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+- New `(lang rocq)` build mode for Rocq 9.0 and later. This new mode
+  is very similar to the existing `(lang coq)`, except that it doesn't
+  need the `coq*` compatibility wrappers. As of today `(lang rocq)`
+  doesn't support yet composed builds with Rocq itself, this will be
+  added later.  `(lang coq)` is deprecated, development is frozen, and
+  will be removed at some point in the future. (#12035, @ejgallego,
+  @lysxia)