This bumps the canary versions to v19 to communicate that the next
release will be a major. Once this lands, we can start merging breaking
changes into `main`.
* Remove object-assign polyfill
We really rely on a more modern environment where this is typically
polyfilled anyway and we don't officially support IE with more extensive
polyfilling anyway. So all environments should have the native version
by now.
* Use shared/assign instead of Object.assign in code
This is so that we have one cached local instance in the bundle.
Ideally we should have a compile do this for us but we already follow
this pattern with hasOwnProperty, isArray, Object.is etc.
* Transform Object.assign to now use shared/assign
We need this to use the shared instance when Object.spread is used.
* Add .browser and .node explicit entry points
This can be useful when the automatic selection doesn't work properly.
* Remove react/index
I'm not sure why I added this in the first place. Perhaps due to how our
builds work somehow.
* Remove build-info.json from files field
This package is missing the license attribute (or a license file).
Being a sub-package of React, it should get the same license, however, none was specified.
A scan with `license_checker` would recognize this as `UNKNOWN`.