Canvas.getMaxDimensions does not work for image api 3.0 (and further)

[nicolasfranck]

The current implementation of method Canvas.getMaxDimensions only returns a Size object for images with api 2.0. It checks for a profile where maxWidth and maxHeight are located, while these properties are located in the root in 3.0.

The question is: should IExternalResource be extended with properties in the root (I cannot check canvas.externalResource.data.maxWidth without resetting the type first to any), or should these
properties from image api 3.0 also be put in the same place (profile), even though that api version
never locates them there.