JS: introduce new flat JS declaration structure

js/js.translator/testData/box/extensionProperty/inClass.kt

@@ -0,0 +1,10 @@
+class A
+
+class B {
+    val A.x: String
+        get() = "OK"
+
+    fun result(a: A) = a.x
+}
+
+fun box() = B().result(A())

js/js.translator/testData/box/inheritance/interfaces/abstractClassInheritingDefaultMethod.kt

@@ -0,0 +1,9 @@
+interface I {
+    fun foo() = "OK"
+}
+
+abstract class A : I
+
+class B : A()
+
+fun box() = B().foo()

js/js.translator/testData/box/inheritance/interfaces/withDefaultMethod.kt

@@ -0,0 +1,7 @@
+interface I {
+    fun foo() = "OK"
+}
+
+class A : I
+
+fun box() = A().foo()

js/js.translator/testData/box/inheritance/interfaces/withDefaultMethodFromSuperInterface.kt

@@ -0,0 +1,9 @@
+interface I {
+    fun foo() = "OK"
+}
+
+interface J : I
+
+class A : J
+
+fun box() = A().foo()

js/js.translator/testData/box/inheritance/interfaces/withDefaultProperty.kt

@@ -0,0 +1,8 @@
+interface I {
+    val foo: String
+        get() = "OK"
+}
+
+class A : I
+
+fun box() = A().foo

js/js.translator/testData/box/native/nativePropertyWithCustomName.kt

@@ -20,7 +20,7 @@ fun box(): String {
     if (foo + bar != OK) return "$foo + $bar != $OK"
 
     val actualAsString = funToString("actual_0")
-    val expectedAsString = funToString("expected_0")
+    val expectedAsString = funToString("expected_0").replace("expected", "actual")
     if (actualAsString != expectedAsString) return "$actualAsString != $expectedAsString"
     if (actual("asd", "12345") != "asd12345") return "${actual("asd", "12345")} != \"asd12345\""