[FE] Prohibit sealed fun interfaces

#KT-44947 Fixed

compiler/testData/diagnostics/tests/sealed/interfaces/sealedFunInterface.kt

@@ -0,0 +1,15 @@
+<!UNSUPPORTED!>sealed<!> fun interface A { // error
+    fun foo()
+}
+
+sealed interface Base {
+    <!UNSUPPORTED!>sealed<!> fun interface Derived : Base {  // error
+        fun foo()
+    }
+}
+
+sealed interface IBase {
+    fun interface IDerived : IBase { // OK
+        fun foo()
+    }
+}