Use `--incremental` flag and `tsBuildInfo` to speed up Quilt CI

[marutypes]

We should be able to leverage tsBuildInfo files to make builds essentially a no-op for libraries that haven't changed, which would help our CI times tremendously.

https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-4.html

[ismail-syed]

For reference, my WIP branch, https://github.com/Shopify/quilt/compare/ts-bump-and-incremental-builds-whyyyy?expand=1