xsettings: Round the Xft.dpi setting to an integer
When using gnome-tweaks to set a text scale factor that is not a multiple of 0.25 (e.g. 1.1), Xft.dpi would be calculated as a floating point number, which breaks the fdo spec:
https://www.freedesktop.org/wiki/Specifications/XSettingsRegistry/
Although GNOME could handle the floating point Xft.dpi, graphical programs restrictively followed the above-mentioned spec would be influenced negatively. For example, QT applications (running on GNOME desktop) may ignore text scaling factor when Xft.dpi was calculated as a floating point number:
https://bugreports.qt.io/browse/QTBUG-64738
The patch at the same time has few impact to GNOME itself.