Companion objects have public visibility by default

#KT-7114 Fixed

compiler/testData/diagnostics/tests/classObjects/companionObjectOfPrivateClassVisibility.kt

@@ -0,0 +1,19 @@
+package test
+
+fun use() {
+    Default.create()
+
+    Explicit.<!INVISIBLE_MEMBER!>create<!>()
+}
+
+private class Default {
+    companion object {
+        fun create() = Default()
+    }
+}
+
+private class Explicit {
+    private companion object {
+        fun create() = Explicit()
+    }
+}