basic multifile class codegen tests

compiler/testData/codegen/boxWithStdlib/platformNames/multifileClass.kt

@@ -0,0 +1,10 @@
+// NB this multifile class should be called "TestPackage" due to the way codegen box tests work.
+@file:JvmName("TestPackage")
+@file:JvmMultifileClass
+package test
+
+fun foo(): String = bar()
+fun bar(): String = qux()
+fun qux(): String = "OK"
+
+fun box(): String = foo()