Port the BAG3 primitives to support the open source PDK

[mithro]

Currently the BAG3 primitives are targetted at the old S8 PDK which is proprietary and only available under NDA from SkyWater. It would be good if these primitives were ported to the SKY130 open source PDK (https://github.com/google/skywater-pdk). The design rules are identical between S8 and SKY130 but the names of the devices and PDK structure has changed.