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/implicitNotNullOnDelegatedImplementation.fir.kt.txt

@@ -52,14 +52,13 @@ class TestJFoo : IFoo {
     super/*Any*/()
     /* <init>() */
 
-    <this>.#<$$delegate_0> = JFoo()
   }
 
   override fun foo(): String {
     return <this>.#<$$delegate_0>.foo()
   }
 
-  local /* final field */ val <$$delegate_0>: IFoo
+  local /* final field */ val <$$delegate_0>: IFoo = JFoo()
 
 }
 
@@ -68,14 +67,13 @@ class TestK1 : IFoo {
     super/*Any*/()
     /* <init>() */
 
-    <this>.#<$$delegate_0> = K1()
   }
 
   override fun foo(): String {
     return <this>.#<$$delegate_0>.foo()
   }
 
-  local /* final field */ val <$$delegate_0>: IFoo
+  local /* final field */ val <$$delegate_0>: IFoo = K1()
 
 }
 
@@ -84,14 +82,13 @@ class TestK2 : IFoo {
     super/*Any*/()
     /* <init>() */
 
-    <this>.#<$$delegate_0> = K2()
   }
 
   override fun foo(): String {
     return <this>.#<$$delegate_0>.foo()
   }
 
-  local /* final field */ val <$$delegate_0>: IFoo
+  local /* final field */ val <$$delegate_0>: IFoo = K2()
 
 }
 
@@ -100,14 +97,13 @@ class TestK3 : IFoo {
     super/*Any*/()
     /* <init>() */
 
-    <this>.#<$$delegate_0> = K3()
   }
 
   override fun foo(): String {
     return <this>.#<$$delegate_0>.foo()
   }
 
-  local /* final field */ val <$$delegate_0>: IFoo
+  local /* final field */ val <$$delegate_0>: IFoo = K3()
 
 }
 
@@ -116,14 +112,13 @@ class TestK4 : IFoo {
     super/*Any*/()
     /* <init>() */
 
-    <this>.#<$$delegate_0> = K4()
   }
 
   override fun foo(): String {
     return <this>.#<$$delegate_0>.foo()
   }
 
-  local /* final field */ val <$$delegate_0>: IFoo
+  local /* final field */ val <$$delegate_0>: IFoo = K4()
 
 }