Box/unbox nullable inline class values with null check

When we have a nullable inline class value with non-null underlying
type, corresponding value in unboxed representation is nullable. E.g.:

  inline class Str(val value: String)

  fun test(s: Str?) = listOf(s)

Here 'test(s: Str?)' accepts nullable 'java.lang.String' as a parameter.

When boxing/unboxing nullable values of such inline classes, take care
of nulls.

 #KT-26052 Fixed Target versions 1.3-M2

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

@@ -1,5 +1,5 @@
 // !LANGUAGE: +InlineClasses
-// IGNORE_BACKEND: JVM_IR, JS_IR, JS
+// IGNORE_BACKEND: JVM_IR, JS
 
 inline class Z(val value: Int)