add wxImage::SetType() and use it in animation decoders (#9639)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@54932 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/image.h

@@ -1027,6 +1027,25 @@ public:
                 unsigned char green,
                 unsigned char blue);
 
+    /**
+        Set the type of image returned by GetType().
+
+        This method is mostly used internally by the library but can also be
+        called from the user code if the image was created from data in the
+        given bitmap format without using LoadFile() (which would set the type
+        correctly automatically).
+
+        Notice that the image must be created before this function is called.
+
+        @since 2.9.0
+
+        @param type
+            One of bitmap type constants, @c wxBITMAP_TYPE_INVALID is a valid
+            value for it and can be used to reset the bitmap type to default
+            but @c wxBITMAP_TYPE_MAX is not allowed here.
+    */
+    void SetType(wxBitmapType type);
+
     /**
         Returns a resized version of this image without scaling it by adding either a
         border