Set implicit size from source size for image/SVG URL sources.
Summary:
This allows users of IconItem to know the aspect ratio of the
source document, which can be used to size the item or set
applet size hints to accomodate non-square images better.
This will be used in a patch to Kicker/Dashboard that ports
a use of Image in its CompactRepresentation to IconItem to
get the hover highlight effect even for a custom button image.
Reviewers: Plasma, mart, davidedmundson
Subscribers: plasma-devel, Frameworks
Tags: Plasma, Frameworks
Differential Revision: https://phabricator.kde.org/D5160