Make UTF-8 decoder follow best practices for U+FFFD substitution
Ensure the vte UTF-8 decoder follows the rules from the W3C Encoding spec for U+FFFD replacement; see also §3.9 subheading "U+FFFD Substitution of Maximal Subparts" of Unicode.
Ensure the vte UTF-8 decoder follows the rules from the W3C Encoding spec for U+FFFD replacement; see also §3.9 subheading "U+FFFD Substitution of Maximal Subparts" of Unicode.