codemod(v6): Convert all process.env usage to dot notation

[dac09]

Process Env Dot Notation

Finds all cases where process.env is accessed via array notation (specifically string literals), and converts it to dot notation.

- process.env['BAZINGA']
+ process.env.BAZINGA

NOTE - this does not deal with dynamic access case. This is something users will need to do themselves

Linting rule for this: #8612

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• Webpack support array notation for both dev and prod
  
  

• Only basic strings work in production. You can't have expressions
  
  

• In Webpack, if you try to access process.env you'll get "MISSING_ENV_VAR" back. But if you try to access an env var that doesn't exist you get undefined (same behavior in both dev and prod)
  
  

• Sometimes you might want to use array notation for tests, like we do in the framework here (it's got red squiggles because I've got our new eslint rule for this set to report it as an error)