Make wxPG_FILE_DIALOG_STYLE a built-in attribute

This attribute is used only internally in wxFileProperty so it can be considered as a built-in attribute which value can be stored in the local data member and not in the property's attribute store.

interface/wx/propgrid/property.h

@@ -151,8 +151,9 @@ struct wxPGPaintData
 */
 #define wxPG_FILE_DIALOG_TITLE              wxS("DialogTitle")
 
-/** Specific to wxFileProperty and derivatives, @c long, default is 0.
-    Sets a specific wxFileDialog style for the file dialog, e.g. ::wxFD_SAVE.
+/** Built-in attribute specific to wxFileProperty and derivatives, @c long,
+    default is 0. Sets a specific wxFileDialog style for the file dialog,
+    e.g. ::wxFD_SAVE.
 
     @since 2.9.4
 */
@@ -617,6 +618,7 @@ wxPG_PROP_CLASS_SPECIFIC_3          = 0x00400000
     given path string.
     - ::wxPG_FILE_INITIAL_PATH: Sets the initial path of where to look for files.
     - ::wxPG_FILE_DIALOG_TITLE: Sets a specific title for the dir dialog.
+    - ::wxPG_FILE_DIALOG_STYLE: Sets a specific wxFileDialog style for the file dialog.
     @see @ref propgrid_property_attributes
 
     @subsection wxEnumProperty

interface/wx/propgrid/props.h

@@ -516,6 +516,8 @@ public:
     given path string.
     - "InitialPath": Sets the initial path of where to look for files.
     - "DialogTitle": Sets a specific title for the dir dialog.
+    - ::wxPG_FILE_DIALOG_STYLE: Sets a specific wxFileDialog style for the file
+    dialog (since 2.9.4).
 */
 class wxFileProperty : public wxPGProperty
 {
@@ -544,10 +546,11 @@ public:
 
 protected:
     wxString    m_wildcard;
-    wxString    m_basePath; // If set, then show path relative to it
-    wxString    m_initialPath; // If set, start the file dialog here
-    wxString    m_dlgTitle; // If set, used as title for file dialog
-    int         m_indFilter; // index to the selected filter
+    wxString    m_basePath;
+    wxString    m_initialPath;
+    wxString    m_dlgTitle;
+    int         m_indFilter;
+    long        m_dlgStyle;
 };