i.e. strict pair of PackageName and LibraryName
the legacy conversion is done via Pretty/Parsec instances.

Change of `Maybe UnqualComponentName` to `LibraryName` caused
a cascade of other changes, but they all seem to be good changes.
In the sense, they made many comments not-so-necessary.

Add Distribution.Types.PackageName.Magic for special package names.

Updates in cabal-install are mostly trivial type error driven changes.
I removed few (deprecated) `Text` instances: `MungedPackageId`,
`MungedPackageName` and `LibraryName`. Turns out only a `Pretty`
part was used, so it was easy to update. Note: `LibraryName`
doesn't have `Pretty` / `Parsec` instances as it's either parsed/printed
as a `ComponentName` or `UnqualComponentName`, never stand alone.