JS: prohibit nested classes, objects and enums in external interface. See KT-16012

compiler/testData/diagnostics/testsWithJsStdLib/native/externalInterfaceNested.kt

@@ -0,0 +1,11 @@
+external interface I {
+    interface J
+
+    class <!NESTED_CLASS_IN_EXTERNAL_INTERFACE!>C<!>
+
+    <!NESTED_CLASS_IN_EXTERNAL_INTERFACE!>object O<!>
+
+    enum class <!NESTED_CLASS_IN_EXTERNAL_INTERFACE!>E<!>
+
+    companion <!NESTED_CLASS_IN_EXTERNAL_INTERFACE!>object<!>
+}

compiler/testData/diagnostics/testsWithJsStdLib/native/externalInterfaceNested.txt

@@ -0,0 +1,49 @@
+package
+
+public external interface I {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    public final class C {
+        public constructor C()
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+
+    public companion object Companion {
+        private constructor Companion()
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+
+    public final enum class E : kotlin.Enum<I.E> {
+        private constructor E()
+        public final override /*1*/ /*fake_override*/ val name: kotlin.String
+        public final override /*1*/ /*fake_override*/ val ordinal: kotlin.Int
+        protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
+        public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: I.E): kotlin.Int
+        public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+        // Static members
+        public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): I.E
+        public final /*synthesized*/ fun values(): kotlin.Array<I.E>
+    }
+
+    public interface J {
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+
+    public object O {
+        private constructor O()
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}

compiler/testData/diagnostics/testsWithJsStdLib/native/optionlBody/native.kt

@@ -12,14 +12,6 @@ external interface T {
 
     fun foo()
     fun bar()
-
-    companion object {
-        val baz: Int
-        val boo: Int = definedExternally
-
-        fun foo()
-        fun bar(): String = definedExternally
-    }
 }
 
 external class C {

compiler/testData/diagnostics/testsWithJsStdLib/native/optionlBody/native.txt

@@ -45,15 +45,4 @@ public external interface T {
     public abstract fun foo(): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
-
-    public companion object Companion {
-        private constructor Companion()
-        public final val baz: kotlin.Int
-        public final val boo: kotlin.Int
-        public final fun bar(): kotlin.String
-        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-        public final fun foo(): kotlin.Unit
-        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
-        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
-    }
 }