Cleanup

- do not use annotation resolve in CodegenFileClassProvider
- test using private methods across different parts of multifile class

compiler/testData/codegen/boxWithJava/fileClasses/multifileClassWithCrossPrivate/foo.kt

@@ -0,0 +1,5 @@
+@file:JvmName("Util")
+@file:JvmMultifileClass
+public fun foo(): String = foox()
+
+private fun barx(): String = "K"