JS: fix non-abstract extension properties in interfaces

KT-20994

compiler/testData/codegen/box/extensionProperties/nonAbstractInInterface.kt

@@ -0,0 +1,19 @@
+interface I {
+    val String.foo: String
+        get() = this + ";" + bar()
+
+    fun bar(): String
+}
+
+class C : I {
+    override fun bar() = "C.bar"
+
+    fun test() = "test".foo
+}
+
+fun box(): String {
+    val r = C().test()
+    if (r != "test;C.bar") return "fail: $r"
+
+    return "OK"
+}