Thumbnails: Make thumbnail generation devicePixelRatio aware
Use the metadata devicePixelRatio to scale up dimensions of thumbnails generated. Sets the devicePixelRatio on the output QPixmap according to the thumbnail generated.
Make the Text Thumbnail creator devicePixelRatio aware.
Follows xdg thumbnail specs 0.9 https://specifications.freedesktop.org/thumbnail-spec/thumbnail-spec-latest.html
It fixes the issue of CacheThumbnail not being respected by the ioslave, it could put in cache thumbnails of text files when they were being used for directory thumbnails.
BUG: 342053 FIXED-IN: 21.08
Requires frameworks/kio!266 (merged)
Prior work: https://phabricator.kde.org/D29526
Edited by Méven Car