AP_RangeFinder: Hexsoon 77G 40M/80M MWW support

[rmackay9]

This adds support for two of the Hexsoon radar:

• HS 776 40M MMW (40m range)
• HS 77G 80M MMW (80m range)

This has been lightly tested on real hardware

A few questions that will likely come up as part of the review:

1. The radar provides distances for 3 sectors similar to some other drivers should this sensors driver also be a Proximity sensor? Should we try and support using this radar as both a RangeFinder and a Proximity sensor?
2. Does it need to be written in C++ or would Lua be sufficient? I think Hexsoon would prefer it was written in C++ to reduce the barrier for users

This work was sponsored by Hexsoon