[K2] Rewrite condition for EXPECTED_PRIVATE_DECLARATION

...without `isTopLevelOrInsideClass` property. Behavior stays the same,
because in fact we require all `expect` member declarations to be non-private
except constructors and property setter.
Enhance already existing test.

^KT-59899

compiler/testData/diagnostics/tests/multiplatform/headerClass/privateMembers.fir.kt

@@ -1,21 +1,27 @@
 // MODULE: m1-common
 // FILE: common.kt
 
-expect class A {
+expect class A private constructor() {
     <!EXPECTED_PRIVATE_DECLARATION!>private<!> fun foo()
     <!EXPECTED_PRIVATE_DECLARATION!>private<!> val bar: String
     <!EXPECTED_PRIVATE_DECLARATION!>private<!> fun Int.memExt(): Any
 
     <!EXPECTED_PRIVATE_DECLARATION!>private<!> class Nested
+
+    var baz: Any?
+        private set
 }
 
 // MODULE: m1-jvm()()(m1-common)
 // FILE: jvm.kt
 
-actual class A {
+actual class A actual private constructor() {
     private fun foo() {}
     private val bar: String = ""
     actual private fun Int.memExt(): Any = 0
 
     actual private class Nested
+
+    actual var baz: Any? = null
+        private set
 }

compiler/testData/diagnostics/tests/multiplatform/headerClass/privateMembers.kt

@@ -1,21 +1,27 @@
 // MODULE: m1-common
 // FILE: common.kt
 
-expect class A {
+expect class A private constructor() {
     <!EXPECTED_PRIVATE_DECLARATION, EXPECTED_PRIVATE_DECLARATION{JVM}!>private<!> fun foo()
     <!EXPECTED_PRIVATE_DECLARATION, EXPECTED_PRIVATE_DECLARATION{JVM}!>private<!> val bar: String
     <!EXPECTED_PRIVATE_DECLARATION, EXPECTED_PRIVATE_DECLARATION{JVM}!>private<!> fun Int.memExt(): Any
 
     <!EXPECTED_PRIVATE_DECLARATION, EXPECTED_PRIVATE_DECLARATION{JVM}!>private<!> class Nested
+
+    var baz: Any?
+        private set
 }
 
 // MODULE: m1-jvm()()(m1-common)
 // FILE: jvm.kt
 
-actual class A {
+actual class A actual private constructor() {
     private fun <!ACTUAL_MISSING!>foo<!>() {}
     private val <!ACTUAL_MISSING!>bar<!>: String = ""
     actual private fun Int.memExt(): Any = 0
 
     actual private class Nested
+
+    actual var baz: Any? = null
+        private set
 }

compiler/testData/diagnostics/tests/multiplatform/headerClass/privateMembers.txt

@@ -2,7 +2,9 @@
 package
 
 public final expect class A {
+    private constructor A()
     private expect final val bar: kotlin.String
+    public expect final var baz: kotlin.Any?
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     private final expect fun foo(): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
@@ -20,8 +22,9 @@ public final expect class A {
 package
 
 public final actual class A {
-    public constructor A()
+    private constructor A()
     private final val bar: kotlin.String = ""
+    public actual final var baz: kotlin.Any?
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     private final fun foo(): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int