Snap font size and weight have increased in recent builds

[furgo16]

On Ubuntu, both the .deb and current .snap daily builds look visually different than that of the weekly AppImage or the snap in the stable channel. The AppImage/stable snap seem to have a thinner font, and smaller in size. These may or may not be related. But with bold text in the .snap/.deb daily build, the font is considerably thicker, which makes it hard to read in places such as the Property Editor.

Below is a comparison screenshot: left is AppImage, right is daily .snap (.deb is the same):

This started happening after #154. Currently the snap in the stable channel looks very much like the AppImage.

Research and tests

• I don't think it's theme-related (both screenshots use FreeCAD Light, but the effect is visible on any theme).
• Setting the QT_SCALE_FACTOR to be smaller than 1.0 scales the whole UI, including the font. It seems to break the UI as well, unless the value is > 1.0.
• Setting QT_FONT_DPI seem to make a difference on the font size, but not on its thickness. On my system, QT_FONT_DPI=85 seems to be the closest in size to the font of the AppImage.
• This old launchpad bug states:

  I changed font hinting to light (default in Kubuntu seems to be medium) and it seems to have solved bugs

• I wonder if the same font is used, but a different weight.
• The kf5-core22 snap package we're using has a /snap/kf5-core22/current/etc/fonts/ folder, with a fonts.conf file. However, when comparing the contents to the old kf5-5-108-qt-5-15-10-core22 snap we were using before Update snap to work with Snapcraft 8.6.0 #154, they seem to be the same.
• This might be related to the changes in the Ubuntu font on 24.04: https://discourse.ubuntu.com/t/ubuntu-24-04-lts-noble-numbat-release-notes/39890 - however, it does not explain why the stable channel snap looks fine and the edge channel does not.
• This seems also related: https://www.reddit.com/r/Kubuntu/comments/1gldhvq/bold_text_in_qt_apps_is_too_bold_and_blurry_after/