Make overloading resolution work for embedded type params

Make overloading resulution work in the case where type parameters follow
value parameters.

Author: odersky

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -1929,7 +1929,7 @@ trait Applications extends Compatibility {
     else
       val deepPt = pt.deepenProto
       deepPt match
-        case pt @ FunProto(_, resType: FunProto) =>
+        case pt @ FunProto(_, resType: FunOrPolyProto) =>
           // try to narrow further with snd argument list
           resolveMapped(candidates, skipParamClause(pt.typedArgs().tpes), resType)
         case _ =>

tests/pos/extmethods.scala

@@ -45,3 +45,13 @@ object CC extends TT:
   val m = Nil
 
 val xx = CC.foo(List(1, 2, 3))
+
+extension (x: TT)
+  def ff[X](): Int = 1
+  def ff[X](s: String): Int = s.length
+  def ff[X](n: Int): Int = n
+
+val yy =
+  CC.ff[Int]()
+  + CC.ff[String]("abc")
+  + CC.ff[Int](22)