feat(shields): Add tester_xiao layouts
Added two layouts for the XIAO tester shield:
- Keys arranged to match the XIAO pinout, viewed from the front
- Single row of eleven keys
These layouts are abstractions since the tester_xiao shield may be
used in a situation where the "keys" are actually jumper wires on a
breadboard or the like.
feat(shields): Add tester_pro_micro layouts
Added two layouts for the Pro Micro tester shield:
- Keys arranged to match the Pro Micro pinout, viewed from the front
- Single row of eighteen keys