Move the fpdfsdk/include/javascript folder

This CL splits the IJavaScript.h file into the two inner classes and puts them
in the fpdfsdk/javascript folder.

Review URL: https://codereview.chromium.org/1847583004
diff --git a/fpdfsdk/javascript/JS_Object.cpp b/fpdfsdk/javascript/JS_Object.cpp
index 9bfa857..d85cc1d 100644
--- a/fpdfsdk/javascript/JS_Object.cpp
+++ b/fpdfsdk/javascript/JS_Object.cpp
@@ -6,10 +6,9 @@
 
 #include "fpdfsdk/javascript/JS_Object.h"
 
-#include "fpdfsdk/include/fsdk_mgr.h"  // For CPDFDoc_Environment.
-#include "fpdfsdk/include/javascript/IJavaScript.h"
-#include "fpdfsdk/javascript/JS_Context.h"
+#include "fpdfsdk/include/fsdk_mgr.h"
 #include "fpdfsdk/javascript/JS_Define.h"
+#include "fpdfsdk/javascript/cjs_context.h"
 
 namespace {