PPX: Add attributes for pointing out interesting nodes for merlin
PPX: Add attributes for pointing out interesting nodes for merlin

Produced typedtrees are ambiguous as multiple nodes are generated for
at the same location.  This attribute helps merlin in choosing the
relevant one for completion, navigation, etc.

alainfrisch/js_of_ocaml,alainfrisch/js_of_ocaml,alainfrisch/js_of_ocaml,alainfrisch/js_of_ocaml,alainfrisch/js_of_ocaml