Fix == for inline classes with boxes

TODO generalize code generating object vs primitive equality

 #KT-25914 Fixed
 #KT-25981 Fixed
 #KT-25983 Fixed

compiler/testData/codegen/box/inlineClasses/inlineClassWithCustomEquals.kt

@@ -0,0 +1,14 @@
+// !LANGUAGE: +InlineClasses
+// IGNORE_BACKEND: JVM_IR
+
+inline class Z(val data: Int) {
+    override fun equals(other: Any?): Boolean =
+        other is Z &&
+                data % 256 == other.data % 256
+}
+
+fun box(): String {
+    if (Z(0) != Z(256)) throw AssertionError()
+
+    return "OK"
+}