Partial revert asSeenFrom

It caused a pattern match exhaustivity test to fail. Now
reducing to the narrowest condition to make opaque aliases work.

Author: odersky

compiler/src/dotty/tools/dotc/core/TypeOps.scala

@@ -53,7 +53,7 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
         tp match {
           case tp: NamedType =>
             val sym = tp.symbol
-            if (sym.isStaticOwner || (tp.prefix `eq` NoPrefix)) tp
+            if (sym.isStatic && !sym.maybeOwner.isOpaqueCompanion || (tp.prefix `eq` NoPrefix)) tp
             else derivedSelect(tp, atVariance(variance max 0)(this(tp.prefix)))
           case tp: ThisType =>
             toPrefix(pre, cls, tp.cls)