JS: refactor flat declaration generator. Add more tests on inter-module dependencies

js/js.translator/testData/box/crossModuleRef/topLevelExtension.kt

@@ -0,0 +1,42 @@
+// MODULE: lib
+// FILE: lib.kt
+
+package lib
+
+class A(val x: Int)
+
+fun A.foo() = 23 + x
+
+inline fun A.baz() = 99 + x
+
+inline fun A.callFoo() = foo()
+
+inline fun A.buzz(): Int {
+    val o = object {
+        fun f() = 111 + x
+    }
+    return o.f()
+}
+
+// MODULE: main(lib)
+// FILE: main.kt
+
+package main
+
+import lib.*
+
+fun box(): String {
+    val a = A(1).foo()
+    if (a != 24) return "fail: simple function: $a"
+
+    val c = A(1).baz()
+    if (c != 100) return "fail: inline function: $c"
+
+    val d = A(1).buzz()
+    if (d != 112) return "fail: inline function with object expression: $d"
+
+    val e = A(2).callFoo()
+    if (e != 25) return "fail: inline function calling another function: $e"
+
+    return "OK"
+}