Manifests are using incorrect axis values

[jvgaultney]

The axis values in fontmanifest.json files are using the output rather than input axis values from the designspace.

Each <instance> in the designspace has an xvalue for each axis that specifies where it is in the design ("output") coordinate space. However the axis location in the font - and in the fontmanifest.json file must be converted to the user ("input") coordinate space value by looking it up in <axes><axis><map>.