[woff2] Optimize table tagging.

Fixes #1107.

* include/freetype/internal/wofftypes.h (WOFF2_TableRec): Use
32-bit tag.
* src/sfnt/sfwoff2.c (compare_tags, find_table, woff2_open_font):
Use 32-bit tag.
* src/sfnt/woff2tags.[ch] (woff2_known_tags): Use static storage and
return 32-bit tag.
4 files changed