[Fontconfig] Changing to hintslight globally by default + hintfull for otfs

[Jerry Casiano]

> You mean, do something like x-and-y-if-supported-native-hinter = 
> hintfull, y-only-native-hinter = medium, y-only-autohinter = slight? 
> That might work just as well. In case that's what it already means, 
> it needs to be better documented.

That's exactly what I meant. And if the result is improved or more
consistent rendering then it's win/win.

Another option is to deprecate those properties and remap them to the
new behavior.

I think that's preferable to breaking compatibility. But I'm just a
consumer concerned about how much would break/need updating. 

> True, but only partly. People have strong opinions about what looks
> best 
> to them, but this is more about jarring differences in hinting
> behavior 
> and output quality. ...

Agreed.