Bump remaining build-time Babel deps

Summary:
Update `babel/*` dependencies specifying `^7.x.y` where `x > 0` to the latest available semver minor, and corresponding superficial snapshot updates reflecting a small decrease in JS bundle size.

 - `babel/core` to `^7.20.0`
 - `babel/parser` to `^7.20.0`
 - `babel/preset-env` to `^7.20.0`
 - `babel/traverse` to `^7.20.0`
 - `babel/cli` to `^7.19.0`
 - `babel/eslint-parser` to `^7.19.0`
 - `babel/preset-flow` to `^7.18.0`
 - `babel/preset-syntax-flow` to `^7.18.0`
 - Deduplicate / refresh others to take in patch updates

Changelog: [Internal] Bump Babel dependencies to latest 7.x

Reviewed By: JoeyMou

Differential Revision: D41449678

fbshipit-source-id: f04fe837a7961c4e2dde45fed59fcd138c2f8723