Added tests on labels

#KT-1703 Fixed
 #KT-361 Fixed
 #KT-3920 Fixed
 #KT-3988 Fixed
 #KT-4247 Fixed
 #KT-4586 Fixed
 #KT-4603 Fixed
 #KT-591 Fixed

compiler/testData/diagnostics/tests/labels/kt4586.kt

@@ -0,0 +1,17 @@
+// !DIAGNOSTICS: -UNUSED_VARIABLE
+//KT-4586 this@ does not work for builders
+
+fun string(init: StringBuilder.() -> Unit): String{
+    val answer = StringBuilder()
+    answer.init()
+    return answer.toString()
+}
+
+val str = string @l{
+    append("hello, ")
+
+    val sub = string {
+        append("world!")
+        this@l.append(this)
+    }
+}