Accept TT_PLATFORM_MICROSOFT, TT_MS_ID_SYMBOL_CS from name table

The OT spec says:

"When building a Unicode font for Windows, the platform ID should be 3 and the
encoding ID should be 1. When building a symbol font for Windows, the platform
ID should be 3 and the encoding ID should be 0."

We were ignoring the SYMBOL_CS entry before.  It's UTF-16/UCS-2 like the
UNICODE_CS.

Also, always use UTF-16BE instead of UCS-2BE.  The conversion was doing
UTF-16BE anyway.