[JS BE] Make properties configurable when implementing an interface by delegation

#KT-42364 Fixed

js/js.translator/src/org/jetbrains/kotlin/js/translate/declaration/DelegationTranslator.kt

@@ -194,6 +194,7 @@ class DelegationTranslator(
         }
         else {
             val literal = JsObjectLiteral(true)
+            literal.propertyInitializers += JsPropertyInitializer(JsStringLiteral("configurable"), JsBooleanLiteral(true))
             literal.propertyInitializers.addGetterAndSetter(descriptor, ::generateDelegateGetter, ::generateDelegateSetter)
             context().addAccessorsToPrototype(classDescriptor, descriptor, literal)
         }

js/js.translator/testData/box/propertyAccess/configurable.kt

@@ -1,4 +1,4 @@
-// EXPECTED_REACHABLE_NODES: 1325
+// EXPECTED_REACHABLE_NODES: 1345
 // KJS_WITH_FULL_RUNTIME
 package foo
 
@@ -15,11 +15,18 @@ class P : EP {
         get() = true
 }
 
+class PD : EP by P()
+
 fun usages() {
     val p = P()
     assertEquals(13, p.simpleProp)
     assertEquals("42", p.anotherProp)
     assertEquals(true, p.propWithGetter)
+
+    val pd = PD()
+    assertEquals(13, pd.simpleProp)
+    assertEquals("42", pd.anotherProp)
+    assertEquals(true, pd.propWithGetter)
 }
 
 fun box(): String {
@@ -31,6 +38,12 @@ fun box(): String {
     assertTrue(isConfigurable(prototype, "anotherProp"))
     assertTrue(isConfigurable(prototype, "propWithGetter"))
 
+    val delegatePrototype = PD::class.js.asDynamic().prototype
+
+    assertTrue(isConfigurable(delegatePrototype, "simpleProp"))
+    assertTrue(isConfigurable(delegatePrototype, "anotherProp"))
+    assertTrue(isConfigurable(delegatePrototype, "propWithGetter"))
+
     return "OK"
 }