MCU: handle custom application fonts and global font properties

MCU applications typically only use fonts that have been explicitly added to the project. System fonts are currently not available to MCU projects unless the user copies the font file into the project folder and declares it with "FontFiles" in the .qmlproject

QDS must be able to handle this behavior for MCU projects.

Acceptance criteria:

• QDS can read and interpret the MCU application's FontFiles as well as MCU.Config.addDefaultFonts and MCU.Config.defaultFontFamily
• The font picker used for font properties in the 2D Editor shows all available fonts for the current project, based on what has been read from the qmlproject: only default fonts, only custom fonts, or both
• In the property panel, when font properties have not explicitly been set, they must display the correct default value, matching what is actually the default in QUL and what has been configured in the qmlproject
• All FontFiles configured in the qmlproject are known to the QDS runtime so that the 2D form editor and the preview use the correct fonts
• The correct default font is used in the 2D form editor and preview