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/nullableEqeqNonNull.kt

@@ -0,0 +1,20 @@
+// !LANGUAGE: +InlineClasses
+// IGNORE_BACKEND: JVM_IR, JS_IR, JS
+
+inline class Z(val value: Int)
+
+fun eq(a: Z?, b: Z) = a == b
+
+fun eqq(a: Z, b: Z?) = a == b
+
+fun box(): String {
+    if (!eq(Z(1), Z(1))) throw AssertionError()
+    if (eq(Z(1), Z(2))) throw AssertionError()
+    if (eq(null, Z(0))) throw AssertionError()
+
+    if (!eqq(Z(1), Z(1))) throw AssertionError()
+    if (eqq(Z(1), Z(2))) throw AssertionError()
+    if (eqq(Z(0), null)) throw AssertionError()
+
+    return "OK"
+}