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/DelegationAndInheritanceFromJava.fir.txt

@@ -6,9 +6,6 @@ FILE fqName:<root> fileName:/DelegationAndInheritanceFromJava.kt
       BLOCK_BODY
         DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in kotlin.Any'
         INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:Impl modality:FINAL visibility:public superTypes:[<root>.Foo.A; <root>.Foo.B]'
-        SET_FIELD 'FIELD DELEGATE name:<$$delegate_0> type:<root>.Foo.B visibility:local [final]' type=kotlin.Unit origin=EQ
-          receiver: GET_VAR '<this>: <root>.Impl declared in <root>.Impl' type=<root>.Impl origin=null
-          value: GET_VAR 'b: <root>.Foo.B declared in <root>.Impl.<init>' type=<root>.Foo.B origin=null
     FUN DELEGATED_MEMBER name:add visibility:public modality:OPEN <> ($this:<root>.Impl, element:kotlin.String?) returnType:kotlin.Boolean
       overridden:
         public abstract fun add (element: E of kotlin.collections.MutableSet): kotlin.Boolean declared in kotlin.collections.MutableSet
@@ -124,6 +121,8 @@ FILE fqName:<root> fileName:/DelegationAndInheritanceFromJava.kt
               $this: GET_FIELD 'FIELD DELEGATE name:<$$delegate_0> type:<root>.Foo.B visibility:local [final]' type=<root>.Foo.B origin=null
                 receiver: GET_VAR '<this>: <root>.Impl declared in <root>.Impl.<get-size>' type=<root>.Impl origin=null
     FIELD DELEGATE name:<$$delegate_0> type:<root>.Foo.B visibility:local [final]
+      EXPRESSION_BODY
+        GET_VAR 'b: <root>.Foo.B declared in <root>.Impl.<init>' type=<root>.Foo.B origin=null
     FUN FAKE_OVERRIDE name:equals visibility:public modality:OPEN <> ($this:kotlin.Any, other:kotlin.Any?) returnType:kotlin.Boolean [fake_override,operator]
       overridden:
         public open fun equals (other: kotlin.Any?): kotlin.Boolean [operator] declared in kotlin.Any