Refactor platform reexports into explicit reexports

[orballo]

Proposed changes

Refactor reexports from platforms/dom.js and platforms/native.js into explicit reexports.

Why

While trying to build my project with parcel and rollup I run into a situation where the bundlers cannot resolve the exports of these files. It has been a bit of a pain. As far as I know, parcel doesn't allow to manually fix this. On the other hand, rollup used to allow a manual fix with an option called namedExports which was deprecated in recent versions and it's no longer available.

Here is an example of the error I get from parcel (note: this only happens with parcel when using the --experimental-scope-hoisting flag, or with parcel v2):

🚨  ../node_modules/@risingstack/react-easy-state/dist/react-platform.js does not export 'unstable_batchedUpdates'
    at replaceExportNode (/Users/orballo/Code/mori/node_modules/parcel/src/scope-hoisting/concat.js:55:13)
    at ReferencedIdentifier (/Users/orballo/Code/mori/node_modules/parcel/src/scope-hoisting/concat.js:342:20)
    at newFn (/Users/orballo/Code/mori/node_modules/@babel/traverse/lib/visitors.js:220:17)
    at NodePath._call (/Users/orballo/Code/mori/node_modules/@babel/traverse/lib/path/context.js:55:20)
    at NodePath.call (/Users/orballo/Code/mori/node_modules/@babel/traverse/lib/path/context.js:42:17)
    at NodePath.visit (/Users/orballo/Code/mori/node_modules/@babel/traverse/lib/path/context.js:90:31)
    at TraversalContext.visitQueue (/Users/orballo/Code/mori/node_modules/@babel/traverse/lib/context.js:112:16)
    at TraversalContext.visitSingle (/Users/orballo/Code/mori/node_modules/@babel/traverse/lib/context.js:84:19)
    at TraversalContext.visit (/Users/orballo/Code/mori/node_modules/@babel/traverse/lib/context.js:140:19)
    at Function.traverse.node (/Users/orballo/Code/mori/node_modules/@babel/traverse/lib/index.js:84:17)

Regarding rollup I found this issue (rollup/rollup#2671). After asking, they suggested that all the reexports should be explicit to avoid this kind of problems.

I'm not sure if this is the ideal solution (I wasn't able to fix it in any other way, though), but if it has no downsides, this changes will at least prevent some pain.

Let me know what you think or if I need to do any further changes.

[rolandszoke]

@orballo Thanks for the fix! 🚀 We will merge your commits to the temp branch along with other changes, so we can make sure everything works fine (tests and build process), and eventually (probably this week) we will release it to alpha.