Add explicit float conversions

[vouillon]

This will eventually be mandatory for compatibility with Wasm_of_ocaml.

[maxtori]

Thanks!
What branch of js_of_ocaml/wasm_of_ocaml are you using to check the deprecation? I probably need to change these points in a lot of projects.

[vouillon]

You can either install js_of_ocaml from the wasm_of_ocaml repository or from ocsigen/js_of_ocaml#1650. The second option is simpler since you don't need to update dune.
You will get type errors if you don't use the Js_of_ocaml library properly, but not from your own bindings if they are using type float instead of Js.number_t. But you can grep for the type float.