Make `Omit` alias its own mapped type so that references to it never expand to `Pick<...>`.
Make `Omit` alias its own mapped type so that references to it never expand to `Pick<...>`.

Microsoft/TypeScript,nojvek/TypeScript,minestarks/TypeScript,nojvek/TypeScript,weswigham/TypeScript,RyanCavanaugh/TypeScript,nojvek/TypeScript,kpreisser/TypeScript,kpreisser/TypeScript,kitsonk/TypeScript,alexeagle/TypeScript,minestarks/TypeScript,kpreisser/TypeScript,microsoft/TypeScript,SaschaNaz/TypeScript,alexeagle/TypeScript,microsoft/TypeScript,weswigham/TypeScript,Microsoft/TypeScript,kitsonk/TypeScript,alexeagle/TypeScript,nojvek/TypeScript,Microsoft/TypeScript,SaschaNaz/TypeScript,weswigham/TypeScript,microsoft/TypeScript,kitsonk/TypeScript,SaschaNaz/TypeScript,RyanCavanaugh/TypeScript,RyanCavanaugh/TypeScript,minestarks/TypeScript,SaschaNaz/TypeScript