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/BUILD.gn b/BUILD.gn
index a4ea471..4b5edbb 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -301,18 +301,25 @@
     "core/fpdfapi/fpdf_cmaps/Korea1/cmaps_korea1.cpp",
     "core/fpdfapi/fpdf_cmaps/cmap_int.h",
     "core/fpdfapi/fpdf_cmaps/fpdf_cmaps.cpp",
+    "core/fpdfapi/fpdf_edit/cpdf_pagecontentgenerator.cpp",
     "core/fpdfapi/fpdf_edit/editint.h",
-    "core/fpdfapi/fpdf_edit/fpdf_edit_content.cpp",
     "core/fpdfapi/fpdf_edit/fpdf_edit_create.cpp",
     "core/fpdfapi/fpdf_edit/fpdf_edit_doc.cpp",
     "core/fpdfapi/fpdf_edit/fpdf_edit_image.cpp",
     "core/fpdfapi/fpdf_edit/include/cpdf_creator.h",
+    "core/fpdfapi/fpdf_edit/include/cpdf_pagecontentgenerator.h",
     "core/fpdfapi/fpdf_font/font_int.h",
     "core/fpdfapi/fpdf_font/fpdf_font.cpp",
     "core/fpdfapi/fpdf_font/fpdf_font_charset.cpp",
     "core/fpdfapi/fpdf_font/fpdf_font_cid.cpp",
     "core/fpdfapi/fpdf_font/ttgsubtable.cpp",
     "core/fpdfapi/fpdf_font/ttgsubtable.h",
+    "core/fpdfapi/fpdf_page/cpdf_form.cpp",
+    "core/fpdfapi/fpdf_page/cpdf_pageobjectholder.cpp",
+    "core/fpdfapi/fpdf_page/cpdf_pageobjectlist.cpp",
+    "core/fpdfapi/fpdf_page/cpdf_pageobjectlist.h",
+    "core/fpdfapi/fpdf_page/cpdf_parseoptions.cpp",
+    "core/fpdfapi/fpdf_page/cpdf_parseoptions.h",
     "core/fpdfapi/fpdf_page/fpdf_page.cpp",
     "core/fpdfapi/fpdf_page/fpdf_page_colors.cpp",
     "core/fpdfapi/fpdf_page/fpdf_page_doc.cpp",
@@ -323,6 +330,9 @@
     "core/fpdfapi/fpdf_page/fpdf_page_parser_old.cpp",
     "core/fpdfapi/fpdf_page/fpdf_page_path.cpp",
     "core/fpdfapi/fpdf_page/fpdf_page_pattern.cpp",
+    "core/fpdfapi/fpdf_page/include/cpdf_form.h",
+    "core/fpdfapi/fpdf_page/include/cpdf_page.h",
+    "core/fpdfapi/fpdf_page/include/cpdf_pageobjectholder.h",
     "core/fpdfapi/fpdf_page/pageint.h",
     "core/fpdfapi/fpdf_parser/cfdf_document.cpp",
     "core/fpdfapi/fpdf_parser/cpdf_array.cpp",
@@ -390,7 +400,6 @@
     "core/fpdfapi/include/cpdf_modulemgr.h",
     "core/fpdfapi/ipdf_pagemodule.h",
     "core/fpdfapi/ipdf_rendermodule.h",
-    "core/include/fpdfapi/fpdf_page.h",
     "core/include/fpdfapi/fpdf_pageobj.h",
     "core/include/fpdfapi/fpdf_resource.h",
   ]