Fix dirty gasoline spawned in lumber mills

[BrettDong]

Summary

SUMMARY: Bugfixes "Fix dirty gasoline obtained from gas pumps in lumber mills"

Purpose of change

Fix #46483. Gasoline spawned in gas pumps in lumber mills contain DIRTY flag and cannot be used to refill vehicles.

Describe the solution

In current implementation place_liquids is applied before setting terrain. Although t_gas_pump has LIQUIDCONT flag, when gasoline is placed, the terrain is not set yet, thus item::on_drop marks gasoline spilled DIRTY.

The solution used in this PR is to use gaspumps instead of place_liquids in mapgen JSON.

Describe alternatives you've considered

An alternative solution is to adjust the order of applying mapgen JSON fields in C++ code. But I am not sure if there will be any side effect.

Testing

Before applying this PR, gasoline spawned in lumber mills carry DIRTY flag. After applying this PR, spawn a new lumber mill, and observe that gasoline spawned is no longer DIRTY. Gasoline spawned here can also be used to refill vehicles without error.

[Hirmuolio]

Overmap terrain "s_gas" also has similar looking fuel placement. Maybe that too makes dirty fuel. It puts them inside furniture tanks instead of terrain in case that affects anything.

[BrettDong]

Overmap terrain "s_gas" also has similar looking fuel placement. Maybe that too makes dirty fuel. It puts them inside furniture tanks instead of terrain in case that affects anything.

Gasoline placed inside gas tanks in gas stations is indeed still dirty, but it is not directly accessible by players. When the player hacks the gas station terminal, some amount of dirty gasoline in gas tanks is deducted and the same amount of clean gasoline is spawned in gas pumps. So at the player's end there is no problem.

[PaulBlay]

Are there any other places that need checking? Like military helipad or airports?