This is not a proper fix, but we are more conservative than is strictly
required. I.e. each "branch" must have `type`.

Also as `type` is set, then `main-is` (or module) have to be specified,
because of `validate*` functions.

The `onAllBranches` is wrong. But we can fix (i.e. relax) it for Cabal-2.4

/Note:/
regressions/issue-5055.format: it's broken as there isn't `main-is`
`os(windows) conditional branch in the formatted output.