`Spring.SetSquareBuildingMask` has poor x/z interface

[sprunk]

Bill of materials to be done before starting this ticket:

• awareness of #1579

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It requires you to scale the x/z parameters by 16 (i.e. Game.buildSquareSize) manually. This requirement is obscure and mistake prone. You should be able to specify the actual x/z you want to affect without having to take internal implementation details into account.

[lhog]

Well our x/z interface is not consistent for example: SetMetalAmount() operates on double-square coordinates, while SetMapSquareTerrainType() uses world coordinates. I think we can harmonize everything to use world coordinates, but I don't know how to make this transition smooth.

[sprunk]

Perhaps a new set of interfaces with consistent names? SetPositionBuildMask, SetPositionMetalAmount, SetPositionTerrainType.

[lhog]

Good idea!