Extract font foundry metadata from the OS/2 table

Extract font foundry metadata from the OS/2 table

* src/sfnt.c (sfnt_table_names): Append an entry for OS/2
tables.
(sfnt_read_OS_2_table): New function.
(main): Introduce a new test for the OS/2 table reader.

* src/sfnt.h (sfnt_read_OS_2_table): New declaration.

* src/sfntfont.c (sfnt_decode_foundry_name): Delete function.
(sfnt_enum_font_1): Read the font's OS/2 table and extract the
foundry name from there.  Use `misc' if absent.
(sfntfont_desc_to_entity, sfntfont_open): Cease interning
desc->designer, as that is now a symbol.
(syms_of_sfntfont) <Qmisc>: New defsym Qmisc.  (bug#65865)