Inconsistent character set supported by the default font across platforms

[lvella]

I have developed an application in Linux, and used some smiley emoji characters in the text. When I built it in Windows and macOS, the emoji rendered as a rectangle. I am not sure what can be done on Iced side about this, but having an inconsistent character set supported by the default font across platform harms its portability.

[hecrj]

iced will try to load a system font by default. Thus, until we implement proper font fallback (see #33), the supported character set depends on the system.

If you want a reliable set of supported characters, then I recommend you to embed your own font and provide it to Settings::default_font.