Update babel packages to new @babel/package

[RibbtDev]

I have updated the old package names to the new @babel/__ ones.

The reason:

If you use the old packages with @babel/core v7+ then it gives the error "plugin should return a function not an object".

This change is important as most of the packages are now available in this format. e.g. @babel/preset-react, @babel/preset-env, etc.

[facebook-github-bot]

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[mroch]

whoops, it failed to import.

the babel.md parts of this landed in #7221, which also updated the "presets": ["flow"] line.
one of the two lines in the compiler-babel.md now conflicts, due to #7856 (sorry I saw that one before this one).
#7049 makes a similar fix to use @babel/cli, but also adds @babel/core. i don't know whether it's necessary.
#7933 makes a partial fix to @babel/preset-flow but not @babel/cli.

I'm going to close this one since it needs to be rebased, at least. I'm going to try to resolve all of these this week, though.