Added wxFile::ReadAll() for consistency with wxFFile::ReadAll().

Make it possible to use wxFFile and wxFile interchangeably for simply reading
the entire contents of the file as a string.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72596 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/file.h

@@ -372,6 +372,23 @@ public:
     */
     ssize_t Read(void* buffer, size_t count);
 
+    /**
+        Reads the entire contents of the file into a string.
+
+        @param str
+            Non-@NULL pointer to a string to read data into.
+        @param conv
+            Conversion object to use in Unicode build; by default supposes
+            that file contents is encoded in UTF-8 but falls back to the
+            current locale encoding (or Latin-1 if it is UTF-8 too) if it is
+            not.
+
+        @return @true if file was read successfully, @false otherwise.
+
+        @since 2.9.5
+    */
+    bool ReadAll(wxString* str, const wxMBConv& conv = wxConvAuto());
+
     /**
         Seeks to the specified position.