Fall back to types when looking up data constructors (#18740)wip/ghc-18740-lookup-update

Before this patch, referring to a data constructor in a term-level
context led to a scoping error:

    ghci> id Int
    <interactive>:1:4: error: Data constructor not in scope: Int

After this patch, the renamer falls back to the type namespace
and successfully finds the Int. It is then rejected in the type
checker with a more useful error message:

    <interactive>:1:4: error:
    • Illegal term-level use of the type constructor ‘Int’
        imported from ‘Prelude’ (and originally defined in ‘GHC.Types’)
    • In the first argument of ‘id’, namely ‘Int’
      In the expression: id Int

We also do this for type variables.

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