* Add weapon_info::clone
Copies every member of a weapon class, following ship_info::clone, so a
weapon can be created from another as ship templates do. The
CLONE_UNIQUE_PTR macro moves from ship.cpp to utils/string_utils.h so
both clone functions share it.
* Group weapon_info::clone fields as the struct declares them
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Co-authored-by: Dustinspace217 <[email protected]>