Improve errors for non-existent labels

This patch fixes #17469, by improving matters when you use
non-existent field names in a record construction:
   data T = MkT { x :: Int }
   f v = MkT { y = 3 }

The check is now made in the renamer, in GHC.Rename.Env.lookupRecFieldOcc.

That in turn led to a spurious error in T9975a, which is fixed by
making GHC.Rename.Names.extendGlobalRdrEnvRn fail fast if it finds
duplicate bindings.  See Note [Fail fast on duplicate definitions]
in that module for more details.

This patch was originated and worked on by Alex D (@nineonine)