Move core/include/fpdfapi/fpdf_page.h to correct locations.

This CL splits the fpdf_page.h header into the individual classes and moves
them to the correct core/fpdfapi locations.

R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1805663002 .
diff --git a/fpdfsdk/pdfwindow/PWL_Icon.cpp b/fpdfsdk/pdfwindow/PWL_Icon.cpp
index 6fa65cf..3e5911e 100644
--- a/fpdfsdk/pdfwindow/PWL_Icon.cpp
+++ b/fpdfsdk/pdfwindow/PWL_Icon.cpp
@@ -7,7 +7,7 @@
 #include "fpdfsdk/include/pdfwindow/PWL_Icon.h"
 
 #include "core/fpdfapi/fpdf_parser/include/cpdf_array.h"
-#include "core/include/fpdfapi/fpdf_page.h"
+#include "core/fpdfapi/fpdf_parser/include/cpdf_stream.h"
 #include "fpdfsdk/include/pdfwindow/PWL_Utils.h"
 #include "fpdfsdk/include/pdfwindow/PWL_Wnd.h"