Adds the following function:
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obs_properties_add_font
This function creates a 'font' property to allow selection of a system
font. Implementation by the UI should treat the setting as an obs_data
sub-object with four sub-items:
- face: face name (string)
- style: style name (string)
- size: size (integer)
- flags: font flags (integer)
'flags' can be any combination of the following values:
- OBS_FONT_BOLD
- OBS_FONT_ITALIC
- OBS_FONT_UNDERLINE
- OBS_FONT_STRIKEOUT