[FlorianDenis]

Binds the hb_ot_var named-instance functions, which are already compiled in but weren't exported:

• hb_ot_var_get_named_instance_count()
• hb_ot_var_named_instance_get_subfamily_name_id()
• hb_ot_var_named_instance_get_postscript_name_id()
• hb_ot_var_named_instance_get_design_coords()

Face.getNamedInstances() returns, for each named instance of a variable font, its index, its subfamily name ID, its PostScript name ID when the font has one, and its design coordinates keyed by axis tag:

const instance = face.getNamedInstances()[11];
// { instanceIndex: 11, subfamilyNameId: 269, coords: { wght: 300, wdth: 75 } }
face.getName(instance.subfamilyNameId, "en"); // "Condensed Light"
font.setVariations(instance.coords);

Notes:

• Returns name IDs rather than resolved names, like getAxisInfos() and getColorPalettes(). An absent PostScript name ID (HB_OT_NAME_ID_INVALID) is left out, as getFeatureNameIds() does.
• Coordinates are keyed by axis tag so they line up with getAxisInfos() and can go straight to Font.setVariations(). If a font repeats an axis tag, the coordinate follows the axis that getAxisInfos() reports for that tag (the last one).