Allow class initializer without primary constructor

compiler/testData/diagnostics/tests/secondaryConstructors/classInitializersWithoutPrimary.kt

@@ -0,0 +1,4 @@
+class A {
+    constructor() {}
+    init {}
+}

compiler/testData/diagnostics/tests/secondaryConstructors/classInitializersWithoutPrimary.txt

@@ -0,0 +1,8 @@
+package
+
+internal final class A {
+    public constructor A()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}