Slow down the turning of ships and disable their InstantTurnAngle
Refs: https://trac.wildfiregames.com/ticket/6522
This makes their movement (a bit) more natural
left side curent svn, right side this patch;
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Turn rates were floored to 4 in D4163 to mitigate the useless turning and twisting of large units trying to pathfind.
(See the gif on D4163)
But with the InstantTurnAngle disabled, I can't reproduce that bug (or at least not very easily):
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