Display "Downloaded From" by default, if file supports it

Summary:
FEATURE: 386261

By default, show "Downloaded From" information from files' extended attributes, if present. No change for files without the xattr.

Test Plan:
Tested in KDE Neon. Blew away dolphinrc and baloofileinformationrc, deployed the baloo-widgets change, rebuilt dolphin, downloaded a file using Chromium (which writes the user.xdg.origin.url xattr), opened Dolphin, navigated to the file, selected it, and turned on the Information panel. Downloaded From was visible. It was (correctly) not visible for any other file that lacked the user.xdg.origin.url xattr.

{F5453057}

Reviewers: #dolphin, #frameworks, broulik, dfaure, markg, vhanda

Reviewed By: markg, vhanda

Subscribers: vhanda

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D8527