Summary:
This change restructures the package to try to remove the JS build step from the inner loop. Instead, we have a single `src` directory that we babel transform when using, then apply the same transform inline during prepublish.
At the end, we will be publishing a source directory with Babel transformed TS, JS, and TS declarations.
We do a little spring cleaning when doing this. Fixing up some of the folder/file conventions, and removing the non-export-map fallbacks.
We cannot remove the need for a native build.
Reviewed By: yungsters
Differential Revision: D45682153
fbshipit-source-id: ea2dd75c2dd6e3529b1ef6cf6ac6a64a270049a4
