Refactor due to "extends": [] Array support

[devinrhode2]

tsconfig.json files will soon support arrays inside the "extends" key:
microsoft/TypeScript#29118

I'd imagine this will simplify this project a lot, and make creating typescript configurations much more expressive.

I believe it may be best to re-imagine tsconfig/bases given this new TS feature. I can't imagine migrating from the non-array based setup would be hard. Existing packages would still exist as published, but wouldn't receive any new updates (do they need to be updated?).

_{hype train: https://twitter.com/DevinRhode2/status/1602790036050681858}

[orta]

I think it could allow some of them to be smaller, but hopefully the change may encourage more folks to ship their own tsconfigs too