FIR2IR: change backing field visibility to private

compiler/testData/ir/irText/classes/innerClassWithDelegatingConstructor.fir.txt

@@ -13,7 +13,7 @@ FILE fqName:<root> fileName:/innerClassWithDelegatingConstructor.kt
           DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in kotlin.Any'
           INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:Inner modality:FINAL visibility:public [inner] superTypes:[kotlin.Any]'
       PROPERTY name:x visibility:public modality:FINAL [val]
-        FIELD PROPERTY_BACKING_FIELD name:x type:kotlin.Int visibility:public [final]
+        FIELD PROPERTY_BACKING_FIELD name:x type:kotlin.Int visibility:private [final]
           EXPRESSION_BODY
             GET_VAR 'x: kotlin.Int declared in <root>.Outer.Inner.<init>' type=kotlin.Int origin=INITIALIZE_PROPERTY_FROM_PARAMETER
         FUN DEFAULT_PROPERTY_ACCESSOR name:<get-x> visibility:public modality:FINAL <> ($this:<root>.Outer.Inner) returnType:kotlin.Int
@@ -21,7 +21,7 @@ FILE fqName:<root> fileName:/innerClassWithDelegatingConstructor.kt
           $this: VALUE_PARAMETER name:<this> type:<root>.Outer.Inner
           BLOCK_BODY
             RETURN type=kotlin.Nothing from='public final fun <get-x> (): kotlin.Int declared in <root>.Outer.Inner'
-              GET_FIELD 'FIELD PROPERTY_BACKING_FIELD name:x type:kotlin.Int visibility:public [final]' type=kotlin.Int origin=null
+              GET_FIELD 'FIELD PROPERTY_BACKING_FIELD name:x type:kotlin.Int visibility:private [final]' type=kotlin.Int origin=null
                 receiver: GET_VAR '<this>: <root>.Outer.Inner declared in <root>.Outer.Inner.<get-x>' type=<root>.Outer.Inner origin=null
       CONSTRUCTOR visibility:public <> () returnType:<root>.Outer.Inner
         BLOCK_BODY
@@ -53,3 +53,4 @@ FILE fqName:<root> fileName:/innerClassWithDelegatingConstructor.kt
       overridden:
         public open fun toString (): kotlin.String declared in kotlin.Any
       $this: VALUE_PARAMETER name:<this> type:kotlin.Any
+