Rename fxjse/ to fxjs/ update files to match class names.

This Cl moves the fxjse/ directory to fxjs/ in anticipation of merging in
fpdfsdk/jsapi. In the process the filenames are updated to better match the
class contents. Static methods are moved to anonymous namespaces as possible.

Review-Url: https://codereview.chromium.org/2136213002
diff --git a/fpdfsdk/javascript/ijs_runtime.h b/fpdfsdk/javascript/ijs_runtime.h
index b24a2dd..cae465a 100644
--- a/fpdfsdk/javascript/ijs_runtime.h
+++ b/fpdfsdk/javascript/ijs_runtime.h
@@ -11,7 +11,7 @@
 #include "core/fxcrt/include/fx_system.h"
 
 #ifdef PDF_ENABLE_XFA
-#include "fxjse/include/fxjse.h"
+#include "fxjs/include/fxjse.h"
 #endif  // PDF_ENABLE_XFA
 
 class CPDFDoc_Environment;