[PL][JS] Add test for handling external declarations

^KT-57378

compiler/testData/klibABI/externalDeclarations/lib2/l2.js

@@ -0,0 +1,25 @@
+function ExternalClassInheritedFromAbstractExternalClass() {}
+ExternalClassInheritedFromAbstractExternalClass.prototype = Object.create(AbstractExternalClass.prototype);
+ExternalClassInheritedFromAbstractExternalClass.prototype.abstractFunction = function() {
+    return "ExternalClassInheritedFromAbstractExternalClass.abstractFunction";
+}
+ExternalClassInheritedFromAbstractExternalClass.prototype.removedAbstractFunction = function() {
+    return "ExternalClassInheritedFromAbstractExternalClass.removedAbstractFunction";
+}
+
+function OpenExternalClass() {}
+OpenExternalClass.prototype.function = function() {
+    return "OpenExternalClass.function"
+}
+
+function ExternalInterfaceInheritedFromOpenExternalClass() {}
+ExternalInterfaceInheritedFromOpenExternalClass.prototype = Object.create(OpenExternalClass.prototype);
+ExternalInterfaceInheritedFromOpenExternalClass.prototype.abstractFunction = function() {
+    throw new Error("Calling abstract function ExternalInterfaceInheritedFromOpenExternalClass.abstractFunction");
+}
+
+function ExternalClassInheritedFromExternalInterfaceInheritedFromOpenExternalClass() {}
+ExternalClassInheritedFromExternalInterfaceInheritedFromOpenExternalClass.prototype = Object.create(ExternalInterfaceInheritedFromOpenExternalClass.prototype);
+ExternalClassInheritedFromExternalInterfaceInheritedFromOpenExternalClass.prototype.abstractFunction = function() {
+    return "ExternalClassInheritedFromExternalInterfaceInheritedFromOpenExternalClass.abstractFunction"
+}

compiler/testData/klibABI/externalDeclarations/lib2/l2.kt

@@ -0,0 +1,38 @@
+@Suppress("ABSTRACT_CLASS_MEMBER_NOT_IMPLEMENTED")
+external class ExternalClassInheritedFromAbstractExternalClass : AbstractExternalClass {
+//    override fun abstractFunction(): String
+    override fun removedAbstractFunction(): String
+}
+
+fun ExternalClassInheritedFromAbstractExternalClass.callRemovedFunction() = removedFunction()
+
+class RegularClassInheritedFromAbstractExternalClass : AbstractExternalClass() {
+    override fun abstractFunction() = "RegularClassInheritedFromAbstractExternalClass.abstractFunction"
+    override fun removedAbstractFunction() = "RegularClassInheritedFromAbstractExternalClass.removedAbstractFunction"
+}
+
+fun RegularClassInheritedFromAbstractExternalClass.callRemovedFunction() = removedFunction()
+
+open external class OpenExternalClass {
+    fun function(): String
+}
+
+@Suppress("INTERFACE_WITH_SUPERCLASS")
+external interface ExternalInterfaceInheritedFromOpenExternalClass : OpenExternalClass {
+    fun abstractFunction(): String
+}
+
+external class ExternalClassInheritedFromExternalInterfaceInheritedFromOpenExternalClass : ExternalInterfaceInheritedFromOpenExternalClass {
+    override fun abstractFunction(): String
+}
+
+class RegularClassInheritedFromExternalInterfaceInheritedFromOpenExternalClass :
+    ExternalInterfaceInheritedFromOpenExternalClass,
+    /* Note: Have to explicitly inherit from 'OpenExternalClass' becase otherwise JS codegen sees that
+     * class 'RegularClassInheritedFromExternalInterfaceInheritedFromOpenExternalClass' is inherited only from
+     * interface 'ExternalInterfaceInheritedFromOpenExternalClass' and does not figure out that a bridge has to be
+     * generated for function 'function' inherited from 'OpenExternalClass'.
+     */
+    OpenExternalClass() {
+    override fun abstractFunction(): String = "RegularClassInheritedFromExternalInterfaceInheritedFromOpenExternalClass.abstractFunction"
+}

compiler/testData/klibABI/externalDeclarations/lib2/module.info

@@ -0,0 +1,2 @@
+STEP 0:
+    dependencies: stdlib, lib1