FIR: introduce delegate field initializers

Before this commit we initialized delegate fields in primary constructor,
that could provoke NPE in case delegate is used in initializer of
some property backing field.
Now we initialize delegate fields directly instead.

compiler/testData/ir/irText/firProblems/AnnotationLoader.fir.kt.txt

@@ -56,10 +56,6 @@ class AnnotationLoader {
                 super/*Any*/()
                 /* <init>() */
 
-                <this>.#<$$delegate_0> = visitor
-              }
-
-              override fun visit() {
               }
 
               override fun visitArray(): Visitor? {
@@ -70,7 +66,9 @@ class AnnotationLoader {
                 return <this>.#<$$delegate_0>.visitAnnotation()
               }
 
-              local /* final field */ val <$$delegate_0>: Visitor
+              local /* final field */ val <$$delegate_0>: Visitor = visitor
+              override fun visit() {
+              }
 
             }