Use position for object delta messages

[ephphatha]

In the worst case this ends up increasing the size of the DLevel object by 127*2 bytes (since we now need to track object position in the delta) + map overhead. Having said that deltas are only really needed for objects which actually allow interaction. Decorations no longer get a delta since they never change. Actual network traffic is compressed so should end up about the same in practice.

Static memory usage increases by 127*2+1 bytes unfortunately due to the use of sgRecvBuf. Hard to tell if we even need this chunk of memory to be on the stack given the use in OnLevelData().

fixes #5172

[AJenbo]

Thanks for solving this :)

[glebm]

Getting a warning:

Source/msg.cpp:357:121: warning: operation on ‘src’ may be undefined [-Wsequence-point]
  357 |                 WorldTilePosition objectPosition { static_cast<WorldTileCoord>(*src++), static_cast<WorldTileCoord>(*src++) };
      |                                                                                                                      ~~~^~

[ephphatha]

GCC warns on code that is valid in C++17 but was undefined before that standard, even if the language level is set to a modern version :/

Can use #5181 to avoid the warning

[glebm]

This is actually useful for us because some platforms do not fully support C++17 (only Amiga by now actually)

[AJenbo]

and my PowePC :)