Rename fpdfsdk/fpdfxfa files to match contents

Each of these files contains a single class, rename the file to match the
internal class name.

Review-Url: https://codereview.chromium.org/2385423004
diff --git a/fpdfsdk/cpdfsdk_interform.cpp b/fpdfsdk/cpdfsdk_interform.cpp
index bc6f2d3..a312ce9 100644
--- a/fpdfsdk/cpdfsdk_interform.cpp
+++ b/fpdfsdk/cpdfsdk_interform.cpp
@@ -38,8 +38,8 @@
 
 #ifdef PDF_ENABLE_XFA
 #include "fpdfsdk/cpdfsdk_xfawidget.h"
-#include "fpdfsdk/fpdfxfa/fpdfxfa_doc.h"
-#include "fpdfsdk/fpdfxfa/fpdfxfa_util.h"
+#include "fpdfsdk/fpdfxfa/cpdfxfa_document.h"
+#include "fpdfsdk/fpdfxfa/cxfa_fwladaptertimermgr.h"
 #include "xfa/fxfa/cxfa_eventparam.h"
 #include "xfa/fxfa/xfa_ffdocview.h"
 #include "xfa/fxfa/xfa_ffwidget.h"