Add an entry about "typesVersions" to the handbook

[rbuckton]

It seems like it would be a good fit under Declaration Files > Publishing: https://www.typescriptlang.org/docs/handbook/declaration-files/publishing.html

[orta]

We've got a mention of it in the v2 site: https://www.staging-typescript.org/docs/handbook/declaration-files/publishing.html#version-selection-with-typesversions