Support KClass.companionObject and companionObjectInstance

#KT-7636 Fixed

compiler/testData/codegen/boxWithStdlib/reflection/classes/companionObject.kt

@@ -0,0 +1,20 @@
+import kotlin.reflect.*
+import kotlin.test.*
+
+class A {
+    companion object C
+}
+
+fun box(): String {
+    val obj = A::class.companionObject
+    assertNotNull(obj)
+    assertEquals("C", obj!!.simpleName)
+
+    assertEquals(A.C, A::class.companionObjectInstance)
+    assertEquals(A.C, obj.objectInstance)
+
+    assertNull(A.C::class.companionObject)
+    assertNull(A.C::class.companionObjectInstance)
+
+    return "OK"
+}