Add warning for initializers with obsolete syntax

Expected 'init' keyword before class initializer

idea/testData/checker/AnonymousInitializers.kt

@@ -1,18 +1,18 @@
 trait NoC {
-  <error>{
+  <error>init {
 
   }</error>
 
   val a : Int get() = 1
 
-  <error>{
+  <error>init {
 
   }</error>
 }
 
 class WithC() {
   val x : Int
-  {
+  init {
     $x = 1
     <error>$y</error> = 2
     val <warning>b</warning> = x
@@ -21,7 +21,7 @@ class WithC() {
 
   val a : Int get() = 1
 
-  {
+  init {
     val <warning>z</warning> = <error>b</error>
     val <warning>zz</warning> = x
     val <warning>zzz</warning> = <error>$a</error>