Move the fpdfsdk/include/pdfwindow/ headers into fpdfsdk/pdfwindow.

This CL moves all of the pdfwindow headers to live beside their source files.

R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1823153002 .
diff --git a/BUILD.gn b/BUILD.gn
index cc25e5c..b97d4e5 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -741,40 +741,40 @@
 
 static_library("pdfwindow") {
   sources = [
-    "fpdfsdk/include/pdfwindow/PWL_Button.h",
-    "fpdfsdk/include/pdfwindow/PWL_Caret.h",
-    "fpdfsdk/include/pdfwindow/PWL_ComboBox.h",
-    "fpdfsdk/include/pdfwindow/PWL_Edit.h",
-    "fpdfsdk/include/pdfwindow/PWL_EditCtrl.h",
-    "fpdfsdk/include/pdfwindow/PWL_FontMap.h",
-    "fpdfsdk/include/pdfwindow/PWL_Icon.h",
-    "fpdfsdk/include/pdfwindow/PWL_IconList.h",
-    "fpdfsdk/include/pdfwindow/PWL_Label.h",
-    "fpdfsdk/include/pdfwindow/PWL_ListBox.h",
-    "fpdfsdk/include/pdfwindow/PWL_ListCtrl.h",
-    "fpdfsdk/include/pdfwindow/PWL_Note.h",
-    "fpdfsdk/include/pdfwindow/PWL_ScrollBar.h",
-    "fpdfsdk/include/pdfwindow/PWL_Signature.h",
-    "fpdfsdk/include/pdfwindow/PWL_SpecialButton.h",
-    "fpdfsdk/include/pdfwindow/PWL_Utils.h",
-    "fpdfsdk/include/pdfwindow/PWL_Wnd.h",
     "fpdfsdk/pdfwindow/PWL_Button.cpp",
+    "fpdfsdk/pdfwindow/PWL_Button.h",
     "fpdfsdk/pdfwindow/PWL_Caret.cpp",
+    "fpdfsdk/pdfwindow/PWL_Caret.h",
     "fpdfsdk/pdfwindow/PWL_ComboBox.cpp",
+    "fpdfsdk/pdfwindow/PWL_ComboBox.h",
     "fpdfsdk/pdfwindow/PWL_Edit.cpp",
+    "fpdfsdk/pdfwindow/PWL_Edit.h",
     "fpdfsdk/pdfwindow/PWL_EditCtrl.cpp",
+    "fpdfsdk/pdfwindow/PWL_EditCtrl.h",
     "fpdfsdk/pdfwindow/PWL_FontMap.cpp",
+    "fpdfsdk/pdfwindow/PWL_FontMap.h",
     "fpdfsdk/pdfwindow/PWL_Icon.cpp",
+    "fpdfsdk/pdfwindow/PWL_Icon.h",
     "fpdfsdk/pdfwindow/PWL_IconList.cpp",
+    "fpdfsdk/pdfwindow/PWL_IconList.h",
     "fpdfsdk/pdfwindow/PWL_Label.cpp",
+    "fpdfsdk/pdfwindow/PWL_Label.h",
     "fpdfsdk/pdfwindow/PWL_ListBox.cpp",
+    "fpdfsdk/pdfwindow/PWL_ListBox.h",
     "fpdfsdk/pdfwindow/PWL_ListCtrl.cpp",
+    "fpdfsdk/pdfwindow/PWL_ListCtrl.h",
     "fpdfsdk/pdfwindow/PWL_Note.cpp",
+    "fpdfsdk/pdfwindow/PWL_Note.h",
     "fpdfsdk/pdfwindow/PWL_ScrollBar.cpp",
+    "fpdfsdk/pdfwindow/PWL_ScrollBar.h",
     "fpdfsdk/pdfwindow/PWL_Signature.cpp",
+    "fpdfsdk/pdfwindow/PWL_Signature.h",
     "fpdfsdk/pdfwindow/PWL_SpecialButton.cpp",
+    "fpdfsdk/pdfwindow/PWL_SpecialButton.h",
     "fpdfsdk/pdfwindow/PWL_Utils.cpp",
+    "fpdfsdk/pdfwindow/PWL_Utils.h",
     "fpdfsdk/pdfwindow/PWL_Wnd.cpp",
+    "fpdfsdk/pdfwindow/PWL_Wnd.h",
   ]
   configs += [ ":pdfium_config" ]
 }