MHU: Package thinning/renaming not supported properly

The way multiple home units calculate dependencies currently ignores any thinning/renaming specifications. This feature is rarely used so it doesn't matter too much for testing but will be subtly broken if anyone does try and use it.

See selectHomeUnits in GHC.Unit.State for the start of where needs to be changed. Then the thinning specification needs to be carried all the way through to the Finder logic and applied accordingly.

Documentation - https://downloads.haskell.org/~ghc/8.8.1/docs/html/users_guide/packages.html#thinning-and-renaming-modules

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