Update React modules in jscomp/test

[mununki]

AFAIK, there are react related modules in ReasonML for easy testing, I guess. It seems outdated and causes the build to fail for ppx v4 which annotates the ref type to ReactDOM https://github.com/rescript-lang/syntax/blob/0bbb5f8e30f220c5d6fe7b836d663a7272cbedff/cli/reactjs_jsx_ppx_v3.ml#L41.

Should it be updated or re-allocated?

[cristianoc]

This is a good question -- when to break compatibility with old reason react.
Even though not necessary for 10.0, if a PPX V4 would go in 10.1, it makes sense to break already from 10.0 as a preparation step.

I guess this needs to be spelled out in #5413
So that a breaking notice goes out with the compiler release.

[cristianoc]

Also again, worth asking in the forum that there are no unintended consequences.