[Freeciv-Dev] (PR#12983) Reuse delta generator structs

["Per I. Mathisen" <per@xxxxxxxxxxx>]

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=12983 >

This patch reuses two delta generator structs inside struct game. Doing
this has the following immediate benefits:
 - a ton of forgotten ruleset parameters are sent to the client
 - this framework makes it a lot easier to add ruleset parameters,
   and ensures that they are sent to the client
 - the tedious copy-struct-to-packet code can be reduced to one line:
      game.rules = packet;
   and
      game.control = packet;
   similarly for the client side.
 - it is the right thing to do as it removes duplicated code

The patch is, however, enormous. I do not want to wait very long before
committing it (although given its size I would prefer if someone else
looked over it and committed it instead).

Also, the choice of where to put ruleset variables was a bit arbitrary,
between game_info, ruleset_game and ruleset_control. I tended to choose
game_info since this was the most flexible - and the delta cache ensures
this is not inefficient anyway.

There are some more variables in struct game that can be moved, but I
would rather do that in a later patch...

I am a bit uncertain as to whether we really need the ruleset_control
packet separate from game_info. It looks to me like they can easily be
combined, as long as game_info is sent once before sending rulesets.

(The patch has gotten only minimal testing and proof-reading as of yet.)

  - Per

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