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/classes/delegatedGenericImplementation.fir.kt.txt

@@ -14,7 +14,6 @@ class Test1<E : Any?> : IBase<E> {
     super/*Any*/()
     /* <init>() */
 
-    <this>.#<$$delegate_0> = i
   }
 
   override fun <B : Any?> foo(a: E, b: B) {
@@ -34,7 +33,7 @@ class Test1<E : Any?> : IBase<E> {
       (<this>.#<$$delegate_0>, <this>).<set-x></* null */>(<set-?> = <set-?>)
     }
 
-  local /* final field */ val <$$delegate_0>: IBase<E>
+  local /* final field */ val <$$delegate_0>: IBase<E> = i
 
 }
 
@@ -43,14 +42,8 @@ class Test2 : IBase<String> {
     super/*Any*/()
     /* <init>() */
 
-    <this>.#<$$delegate_0> = j
   }
 
-  var j: IBase<String>
-    field = j
-    get
-    set
-
   override fun <B : Any?> foo(a: String, b: B) {
     <this>.#<$$delegate_0>.foo</* null */>(a = a, b = b)
   }
@@ -68,7 +61,11 @@ class Test2 : IBase<String> {
       (<this>.#<$$delegate_0>, <this>).<set-x></* null */>(<set-?> = <set-?>)
     }
 
-  local /* final field */ val <$$delegate_0>: IBase<String>
+  local /* final field */ val <$$delegate_0>: IBase<String> = j
+  var j: IBase<String>
+    field = j
+    get
+    set
 
 }