chore: make ubergen a library (#23962)

Move the useful stuff in ubergen into lib/index.ts and add `main` field to package json so packages within the repository can depend on it's functionality. Specifically useful for repo restructure work.

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: MrArnoldPalmer