fontface_to_numeric: Convert Fontface String to Numeric
Description
Converts fontface string specification to numeric value used by R graphics.
Handles both string ("plain", "bold", "italic", "bold.italic") and
numeric (1, 2, 3, 4) inputs for backwards compatibility.
Usage
fontface_to_numeric(fontface)
Value
Numeric fontface value (1=plain, 2=bold, 3=italic, 4=bold.italic).