Commits on Nov 5, 2021

1. Try to instantiate type variables in tryInsertImplicitOnQualifier …

   Fixes scala#13842
   
   What happened in scala#13842 was that we were not hitting this case in
   `tryWiden`, which is a method in ApproximatingTypeMap that tries
   to dealias or widen before propagating a Range outwards:
   
   ```scala
             case info: SingletonType =>
               // if H#x: y.type, then for any x in L..H, x.type =:= y.type,
               // hence we can replace with y.type under all variances
               reapply(info)
   ```
   The actual info here was a TypeVar with a singleton type as lower bound. Instantiating
   the TypeVar produces a SingletonType and case applies.
   
   We cannot really instantiate TypeVars here since this is very low-level code. For instance
   we might be in a state where the instantiation is provisional and the TyperState is thrown
   away. But AsSeenFrom results are cached so we'd have the wrong type in the caches.
   
   What we do instead is add an additional case in `tryInsertImplicitOnQualifier` which is the
   last resort when an application fails. Here, if we can instantiate some type variables in the
   qualifier, we try again.

   

   odersky committed Nov 5, 2021
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