Add a proto equivalent to sc2_typeenums.h

https://github.com/Blizzard/s2client-api/blob/master/include/sc2api/sc2_typeenums.h

As sc2_typeeenums.h says, "All units and abilities are represented as unsigned numbers in the StarCraft II engine. This can make issue abilities unnecessarily hard."

This fact is also true with the proto API. As it is, any equivalent implementation of the sc2api client in another language will have to define its own equivalent of these enums, or force its users to figure out the unit indexes themselves.

Is it possible to define this as a protobuf enum as part of the protocol sent by the game?

Start by reading the referenced sc2_typeenums.h and the repository's existing protocol definitions. Compare the unit and ability values with what the proto API currently exposes, then determine the protocol changes needed so equivalent enum information is available to clients. Done means the proto API provides those mappings without requiring each client to recreate them.

Written by the indexing model from the issue text.