JS: add some tests to ensure that AST metadata is correctly serialized and deserialized and visible to JS optimizer

js/js.translator/testData/box/incremental/syntheticStatement.kt

@@ -0,0 +1,25 @@
+/// FILE: a.kt
+
+fun a() = "["
+
+fun b() = "]"
+
+inline fun sideEffect(f: () -> String, g: () -> Unit): String {
+    g()
+    return f()
+}
+
+inline fun foo(f: () -> String, g: () -> Unit): String {
+    return a() + sideEffect(f, g) + b()
+}
+
+
+// FILE: b.kt
+// RECOMPILE
+
+fun box(): String {
+    val result = foo({ "*" }, { })
+    if (result != "[*]") return "fail: $result"
+
+    return "OK"
+}