JS: create new common directory for all generated tests, migrate several tests there

js/js.translator/testData/box/closure/closureThisInExtLambdaInsideMethod.kt

@@ -0,0 +1,9 @@
+// KT-4600 Generated wrong code when capturing `this` in extension function inside a method
+
+package foo
+
+public class Foo(val trigger: () -> Any) {
+    fun test() = myRun { trigger() };
+}
+
+fun box() = Foo({ "OK" }).test()