Add Portable Font Resource `application/font-tdpfr`

Bitstream's TrueDoc Portable Font Resource format is part of several digital TV broadcast specifications and is documented as RFC 3073: https://datatracker.ietf.org/doc/html/rfc3073

   Magic number(s): 50 46 52 30 hex
   File extension(s): PFR
   Macintosh File Type Code(s): Creator: 'b$pw' Type: 'PFR '

There is also a newer version of the format with 50 46 52 31 hex (PFR1), such as the test file included here. libmagic also recognizes PFR1: https://github.com/file/file/blob/7a821aedc144f70ec848ea632a64db74b79563c1/magic/Magdir/fonts#L249-L252

The Bitstream specifications are available from Wayback Machine: https://web.archive.org/web/20040407162455/http://www.bitstream.com/categories/developer/truedoc/pfrspec.html

"The PFR specification defines the Bitstream portable font resource (PFR), which is a compact, platform-independent format for representing high-quality, scalable outline fonts. Many independent organizations responsible for setting digital TV standards have adopted the PFR font format as their standard font format, including:

• ATSC (Advanced Television Systems Committee)
• DAVIC (Digital Audio Visual Council)
• DVB (Digital Video Broadcasting)
• DTG (Digital TV Group)
• MHP (Multimedia Home Platform)
• ISO/IEC 16500-6:1999
• OCAP (OpenCable Application Platform)"

Per RFC 3073, "The PFR media type has been previously registered with IANA as application/vnd.truedoc. In view of its subsequent widespread adoption as a standard font format by multiple standards bodies who have relationships with the Internet community, Bitstream has been asked to re-register this media type within the IETF tree." https://www.iana.org/assignments/media-types/application/vnd.truedoc http://www.iana.org/assignments/media-types/application/font-tdpfr

This format was once supported for downloadable web fonts in Netscape 4.x.