[uniscribe] Use unique font name

When installing per-process fonts using AddFontMemResourceEx(),
if a font with the same family name is already installed, sometimes
that one gets used.  Which is problematic for us.  As such, we
now mangle the font to install a new 'name' table with a unique
name, which we then use to choose the font.

Patch from Jonathan Kew.
[uniscribe] Use blob to pass data around
[uniscribe] Move name generation into separate function
[uniscribe] Use OT::* types