Minor, move builtins serializer test data

compiler/testData/serialization/builtinsSerializer/annotationArguments/string.kt

@@ -0,0 +1,12 @@
+package test
+
+annotation class JustString(val string: String)
+
+annotation class StringArray(val stringArray: Array<String>)
+
+JustString("kotlin")
+StringArray(array())
+class C1
+
+StringArray(array("java", ""))
+class C2