Fix copying of non-abstract functions of interfaces in JS BE

Fix copying of non-abstract functions of interfaces to implementing
classes when implementing class inherits interface via 2+ paths.

See KT-18187

compiler/testData/codegen/box/traits/interfaceWithNonAbstractFunIndirect.kt

@@ -0,0 +1,29 @@
+interface I {
+    fun foo(): String = "foo"
+
+    fun bar(x: String = "default") = "bar:$x"
+}
+
+interface J : I
+
+interface K : J
+
+class A : I, J
+
+class B : K, I
+
+fun box(): String {
+    val foo = A().foo()
+    if (foo != "foo") return "fail1: $foo"
+
+    val bar1 = A().bar()
+    if (bar1 != "bar:default") return "fail2: $bar1"
+
+    val bar2 = A().bar("q")
+    if (bar2 != "bar:q") return "fail3: $bar1"
+
+    val foo2 = B().foo()
+    if (foo2 != "foo") return "fail4: $foo2"
+
+    return "OK"
+}