JS: prohibit overriding external functions with optional parameters by non-external functions. See KT-13889

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

@@ -0,0 +1,32 @@
+open external class A {
+    open fun f(x: Int = noImpl)
+}
+
+class B : A() {
+    <!OVERRIDING_EXTERNAL_FUN_WITH_OPTIONAL_PARAMS!>override fun f(x: Int)<!> {}
+}
+
+external class C : A() {
+    override fun f(x: Int) {}
+}
+
+
+external interface I {
+    fun f(x: Int = noImpl)
+}
+
+open external class D {
+    open fun f(x: Int)
+}
+
+class E : D() {
+    override fun f(x: Int) {}
+}
+
+class F : D(), I {
+    <!OVERRIDING_EXTERNAL_FUN_WITH_OPTIONAL_PARAMS!>override fun f(x: Int)<!> {}
+}
+
+external class G : D(), I {
+    override fun f(x: Int) {}
+}

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

@@ -0,0 +1,64 @@
+package
+
+public external open class A {
+    public constructor A()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open fun f(/*0*/ x: kotlin.Int = ...): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class B : A {
+    public constructor B()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ fun f(/*0*/ x: kotlin.Int = ...): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public external final class C : A {
+    public constructor C()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ fun f(/*0*/ x: kotlin.Int = ...): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public external open class D {
+    public constructor D()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open fun f(/*0*/ x: kotlin.Int): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class E : D {
+    public constructor E()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ fun f(/*0*/ x: kotlin.Int): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class F : D, I {
+    public constructor F()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ fun f(/*0*/ x: kotlin.Int = ...): kotlin.Unit
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public external final class G : D, I {
+    public constructor G()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ fun f(/*0*/ x: kotlin.Int = ...): kotlin.Unit
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public external interface I {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun f(/*0*/ x: kotlin.Int = ...): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}