Use final result type to check selector bound

Author: som-snytt

Diff for: compiler/src/dotty/tools/dotc/transform/CheckUnused.scala

@@ -729,7 +729,7 @@ object CheckUnused:
             if selector.isGiven then
               // Further check that the symbol is a given or implicit and conforms to the bound
               sym.isOneOf(Given | Implicit)
-                && (selector.bound.isEmpty || sym.info <:< selector.boundTpe)
+                && (selector.bound.isEmpty || sym.info.finalResultType <:< selector.boundTpe)
                 && selData.qualTpe =:= prefix
             else
               // Normal wildcard, check that the symbol is not a given (but can be implicit)

Diff for: tests/warn/i19657.scala

@@ -30,3 +30,7 @@ def `i19657 check prefix to pick specific selector`: Unit =
   import FooCodec.given_Schema_A
   import BarCodec.given_Schema_A
   summonSchemas
+
+def `i20860 use result to check selector bound`: Unit =
+  import Ordering.Implicits.given Ordering[?]
+  summon[Ordering[Seq[Int]]]