Add Ampersand Ligature Variant for `ss03` The feature `ss03` changes the ampersand to the traditional style. When this feature is enabled the restyling of the ligature form `ampersand_ampersand.liga` is not used because it does not exist. This commit adds the part glyph `_part.ampersand.ss03`, adds the ligature glyph `ampersand_ampersand.liga.ss03`, and modifies the `ss03` feature to use the newly added ligature when the feature is enabled. The part glyph was only created to be a component for the newly added ligature, like `_part.ampersand` is for `ampersand_ampersand.liga`.