add regression test for issue scala#13021 (scala#20104)

fixes scala#13021

Author: nicolasstucki

tests/pos-macros/i13021/DFBits.scala

@@ -0,0 +1,6 @@
+object DFBits:
+  opaque type Token[W <: Int] <: DFToken.Of[Int] = DFToken.Of[Int]
+  extension [W <: Int](token: Token[W])
+    def data: Int =
+      token.asIR
+      1

tests/pos-macros/i13021/DFToken.scala

@@ -0,0 +1,14 @@
+trait Token:
+  val data: Any
+
+opaque type DFToken = Token
+object DFToken:
+  extension (of: DFToken) def asIR: Token = ???
+
+  opaque type Of[D] <: DFToken = DFToken
+  object Of:
+    extension [D](token: Of[D]) def width(using w: Width[?]): Int = ???
+
+def getWidth[W <: Int](token: DFBits.Token[W]): Int = token.width
+def getData[W <: Int](token: DFBits.Token[W]): Int =
+  token.data //error here

tests/pos-macros/i13021/Width.scala

@@ -0,0 +1,12 @@
+import scala.quoted.*
+
+trait Width[T]:
+  type Out <: Int
+object Width:
+  transparent inline given [T]: Width[T] = ${ getWidthMacro[T] }
+  def getWidthMacro[T](using Quotes, Type[T]): Expr[Width[T]] =
+    '{
+      new Width[T] {
+        type Out = Int
+      }
+    }