UITextIcon does not allow unicode characters to be used

[marvinvis]

I'm using UITextIcon musicIcon = UITextIcon(u8g2_font_siji_t_6x10, UISize(14, 14));

when setting the text using an escape sequence: musicIcon.setText("\xee\x88\x85");

nothing is shown.

however, using a UITextLine with the parameter isUnicode to true, does show the correct symbol (music note) (see 0xe205 in https://github.com/olikraus/u8g2/wiki/fntgrpsiji).

suggestion: allow UITextIcon to be unicode, similar to the UITextLine.