Name class

In the most places in frontend identifier is stored in Name class, was in String.
Name has two advantages over String:
* validation: you cannot accidentally create identifier with dot, for example
* readability: if you see String, you don't now whether it is
  identifier, fq name, jvm class name or something else

Name's disadvantage is (small) performance overhead. We have no value types in JVM.

compiler/testData/renderer/GlobalProperties.kt

@@ -17,4 +17,4 @@ get() {}
 //internal final val int2 : jet.Int defined in rendererTest
 //private final var private : jet.Int defined in rendererTest
 //public final val jet.Int.ext : jet.Int defined in rendererTest
-//public final fun jet.Int.get-ext() : jet.Int defined in rendererTest
+//public final fun jet.Int.<get-ext>() : jet.Int defined in rendererTest