Blurry splash screen and logos, unscaled text with Windows display scaling (e.g. 125%) #460

With a Windows display scaling greater than 100% (e.g., 125%):

• the splash screen, the DataLab logo of the welcome page and of the guided tour, and the watermark of empty plots are blurry;
• most of the text of the user interface (welcome page, object properties, panel tabs, dialog boxes, ...) keeps its 100% size, while menus and the status bar are enlarged.

Causes

• These images exist only as PNG files rendered for a 100% scaling: Qt upscales them by the scaling factor.
• With Qt 5 on Windows, the default application font is derived from the legacy DEFAULT_GUI_FONT stock object, whose pixel size ignores the display scaling, while Qt converts it to points with the DPI of the screen (QTBUG-58610, fixed in Qt 6): at 125%, it ends up at 6.6pt instead of 8.25pt, so that the text keeps its 100% size once scaled. Menus and the status bar use other system fonts, which are scaled correctly. This affects DataLab running with Qt 5, like the standalone application.

Fix

• guidata (Text not scaled with Windows display scaling (Qt 5) and no high-DPI image loading PlotPyStack/guidata#121): with Qt 5 on Windows, use the message font of the system (typically "Segoe UI", 9pt) as default font, like Qt 6 does; new guidata.configtools.get_pixmap function, which uses the @2x high-resolution variants of an image (Qt naming convention) on high-DPI displays.
• SigimaX (Blurry splash screen and plot watermark with display scaling (e.g. 125%) SigimaX#33): the splash screen and the plot watermark are loaded with get_pixmap.
• DataLab: @2x variants of the images displayed by the application (generated by scripts/build_resources.py logo), and the welcome page and guided tour logos are loaded with get_pixmap.