Upgrade to Babel 7.10

Summary:
See https://github.com/babel/babel/releases/tag/v7.10.0 for changes

It includes a change I asked the Babel team for as they have been wrapping object spread calls with lots of extends call for spec compliance, but that only matters when you have side-effectful getters that affect the rest of the objects in the spread call and are order dependent. We should not be depending on such behavior in FB code so we can use loose mode and benefit from the app size wins.

Changelog: [Internal]

Reviewed By: motiz88

Differential Revision: D21738344

fbshipit-source-id: 5eeff47481e474bb41183119d990692b31751dd5