Only private constructors for sealed / enum classes #KT-12377 Fixed

Also #KT-8497 Fixed

compiler/testData/diagnostics/tests/enum/NonPrivateConstructor.kt

@@ -0,0 +1,7 @@
+enum class E <!NON_PRIVATE_CONSTRUCTOR_IN_ENUM!>public<!> constructor(val x: Int) {
+    FIRST();
+
+    <!NON_PRIVATE_CONSTRUCTOR_IN_ENUM!>internal<!> constructor(): this(42)
+
+    constructor(y: Int, z: Int): this(y + z)
+}

compiler/testData/diagnostics/tests/enum/NonPrivateConstructor.txt

@@ -0,0 +1,23 @@
+package
+
+public final enum class E : kotlin.Enum<E> {
+    enum entry FIRST
+
+    internal constructor E()
+    public constructor E(/*0*/ x: kotlin.Int)
+    private constructor E(/*0*/ y: kotlin.Int, /*1*/ z: kotlin.Int)
+    public final override /*1*/ /*fake_override*/ val name: kotlin.String
+    public final override /*1*/ /*fake_override*/ val ordinal: kotlin.Int
+    public final val x: kotlin.Int
+    protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
+    public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: E): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    protected/*protected and package*/ final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun finalize(): kotlin.Unit
+    public final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun getDeclaringClass(): java.lang.Class<E!>!
+    public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): E
+    public final /*synthesized*/ fun values(): kotlin.Array<E>
+}