bug#45133: Add ocaml reactiveData

[Julien Lepiller]

Pushed as 190187326ad7516dd6728eed7bb6ef2d4f92897a.

I made a small number of changes to your patch:

In the commit message, added capitalization (add -> Add) and full
stops, removed spaces at the beginning of the `*` line.

In the patch, added a copyright line for you, added a comment to the
phase where we delete the Makefile, fixed the description (guix lint
should have told you so), and added an upstream-name property so guix
refresh knows where to look for newer versions. In general, it's not
needed because guix-name->opam-name works well, but here we lost
capitalization, so we need to explicitely tell it which name it is.

Thank you!