[meta] Should for-ghc-only releases take up major release numbers?

I am wondering if a better approach, given that these releases are not intended for public use but only for ghc, is to expand our use of devel release numbers: assuming that it's too late to fix this for 3.14, then

- 3.15.0.0 is the first devel version
- 3.15.1.0 would be the first for-ghc release
- 3.15.2.0 would be for continued development after the first for-ghc release
- if needed, we could repeat this with 3.15.3.0/3.15.4.0 and so on.

This way we don't confuse our release numbers, which currently are on course for us to _from a public release standpoint_ skip from 3.12.1.0 to 3.16.0.0.