[FIR] Fix processing constructors of sealed classes

- Allow declaring protected constructors in sealed classes
- Make default visibility of sealed class constructor `protected`

KT-44861
KT-44865

compiler/testData/diagnostics/tests/sealed/protectedConstructors_enabled.fir.kt

@@ -2,21 +2,21 @@
 // DIAGNOSTICS: -UNUSED_PARAMETER
 
 sealed class Case1(val x: Int) {
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+    protected constructor(s: String) : this(s.length)
 
     class Inheritor1 : Case1(10)
     class Inheritor2 : Case1("Hello")
 }
 
-sealed class Case2 <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(val x: Int)<!> { // should be REDUNDANT_MODIFIER
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+sealed class Case2 protected constructor(val x: Int) { // should be REDUNDANT_MODIFIER
+    protected constructor(s: String) : this(s.length)
 
     class Inheritor1 : Case2(10)
     class Inheritor2 : Case2("Hello")
 }
 
 sealed class Case3 private constructor(val x: Int) {
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+    protected constructor(s: String) : this(s.length)
 
     class Inheritor1 : Case3(10) // should OK
     class Inheritor2 : Case3("Hello")
@@ -25,8 +25,8 @@ sealed class Case3 private constructor(val x: Int) {
 class Case3Inheritor3 : <!INAPPLICABLE_CANDIDATE!>Case3<!>(20) // should be an error in 1.6 (?)
 
 sealed class Case4 {
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(x: Int)<!>
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+    protected constructor(x: Int)
+    protected constructor(s: String) : this(s.length)
 
     class Inheritor1 : Case4(10)
     class Inheritor2 : Case4("Hello")
@@ -34,8 +34,8 @@ sealed class Case4 {
 
 sealed class Case5() {
     private constructor(x: Int) : this()
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(x: Byte) : this()<!>
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>internal constructor(x: Short) : this()<!>
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>public constructor(x: Long) : this()<!>
+    protected constructor(x: Byte) : this()
+    <!NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED!>internal constructor(x: Short) : this()<!>
+    <!NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED!>public constructor(x: Long) : this()<!>
     constructor(x: Double) : this()
 }