Fix getInfo in picture adapter

If an automation is used to import an Adobe Illustrator file in DAM (see NXP-14554) the getInfo method is called many times - first for the main document, then for the five view files, and again for the main doc and view files.

This is problematic when working with Illustrator files because getInfo uses the 'identify' command from ImageMagick which has to use ghostscript to do its work, and this is an expensive process.

We should improve the picture adapter so that the getInfo for the main document is cached, and does not need to be recomputed while creating the view files.