Backport "Allow SAM types to contain multiple refinements" to 3.3.4 (#21556)

Backports #20172 to Scala 3.3.4-RC2 as the follow-up to #20092
regression fix.

---------

Co-authored-by: Guillaume Martres <smarter@ubuntu.com>
Co-authored-by: Eugene Flesselle <eugene@flesselle.net>

Author: 3 people

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

@@ -5579,7 +5579,7 @@ object Types extends TypeUtils {
       def withRefinements(toType: Type, fromTp: Type): Type = fromTp.dealias match
         case RefinedType(fromParent, name, info: AliasingBounds) if tp0.member(name).exists =>
           val parent1 = withRefinements(toType, fromParent)
-          RefinedType(toType, name, info)
+          RefinedType(parent1, name, info)
         case _ => toType
       val tp = withRefinements(tp0, origTp)
 

tests/run/i18315.scala

@@ -7,9 +7,16 @@ trait Sam2:
   type T
   def apply(x: T): T
 
+trait Sam3:
+  type T
+  type U
+  def apply(x: T): U
+
 object Test:
   def main(args: Array[String]): Unit =
     val s1: Sam1 { type T = String } = x => x.trim
     s1.apply("foo")
     val s2: Sam2 { type T = Int } = x => x + 1
     s2.apply(1)
+    val s3: Sam3 { type T = Int; type U = String } = x => x.toString
+    s3.apply(2)