[JS IR] Do not copy interface method if base class inherits it

^KT-58599 Fixed

js/js.translator/testData/box/dce/removeUnusedOverride.kt

@@ -0,0 +1,55 @@
+// TARGET_BACKEND: JS_IR
+// ONLY_IR_DCE
+// RUN_PLAIN_BOX_FUNCTION
+// INFER_MAIN_MODULE
+
+// MODULE: remove_unused_override
+// FILE: lib.kt
+
+interface I {
+    fun foo() = "OK"
+}
+
+abstract class A : I
+
+class B : A()
+
+class C : A() {
+    override fun foo(): String {
+        return "C::foo"
+    }
+}
+
+@JsExport
+fun makeB(): A {
+    val b = B()
+    b.foo()
+    return b
+}
+
+@JsExport
+fun makeC(): A {
+    return C()
+}
+
+// FILE: test.js
+function box() {
+    var b = this["remove_unused_override"].makeB()
+    var c = this["remove_unused_override"].makeC()
+
+    var cnt = 0
+    for(var prop in b) {
+        if (typeof b[prop] === 'function' && prop != 'constructor') {
+            ++cnt
+            if (b[prop].call(b) != "OK") return "expect inherited method"
+        }
+    }
+    for(var prop in c) {
+        if (typeof c[prop] === 'function' && prop != 'constructor') {
+            ++cnt
+            if (c[prop].call(c) != "OK") return "override C::foo() should be removed by DCE"
+        }
+    }
+
+    return cnt == 2 ? "OK" : ("Expected 2 calls, got " + cnt)
+}