Map "named characters" to unicode-equivalent characters for output.

[axkr]

Use the unicode-equivalent information about named characters to create a better looking string or operator output:

See:

• https://github.com/Mathics3/mathics-scanner/blob/master/mathics_scanner/data/named-characters.yml

Examples:

\[CapitalDifferentialD]
'\uF74B' => '\u2145'

\[Implies]
'\uF523' =>  '\u21D2'

\[Equivalent]
'\u29E6' =>  '\u21D4'  // DoubleLeftRightArrow