Add: support for stations

[glx22]

It's finally possible to create stations newgrf with NML.
I implemented most props, but I'm not sure about their naming or simplicity of use. Maybe more global constants are needed.
I think I correctly implemented sprite layout for stations (was the hardest part).
I added a SPRITESET() function existing only for stations, used to refer to active spriteset (the one selected with basic action2).
Custom foundations are also implemented.
I tested many things locally and it works for me.

As an example, I converted CHIPS Cow pens station (and yes there are blinking cows 🐮🤣).
Regression test also produces a working grf.

[glx22]

copy_sprite_layout can't work in the current implementation. I need to rethink things.

[frosch123]

Not sure about the name here.
The result indexes into the properties "draw_pylon_tiles", "hide_wire_tiles" and "non_traversable_tiles".
So maybe "select_tile_index", "select_tile_type" or just "select_tille"?

[glx22]

Yeah naming is hard.

[frosch123]

If property 0E is not supported/needed, I don't think these constants are useful either.

[glx22]

Only use I can see would be in bitmask() for hide_wire_tiles or non_traversable_tiles, so yeah probably useless.

[andythenorth]

CHIPS port in progress to test this: https://github.com/andythenorth/chips/tree/nml-port

[glx22]

I did some test trying to port CHIPS 'magic' stations.
Found some issues:

• it's not possible to use LOAD_TEMP() in the layout, because the STORE_TEMP() will happen after registers are set (registers action2 is inserted in front of any action3 result)
• some callbacks need a purchase specific version (at least select_sprite_layout)

[glx22]

Fixed the 2 issues I noticed (and reworked some part for the third time)

[glx22]

SPRITESET([offset]) renamed to DEFAULT([offset]).
Added CUSTOM(index, [offset]), with index pointing into custom_spritesets array.
Advanced test using most of the implemented stuff is available here.

Purchase/non-purchase splitting for callbacks may not be enough. Originally CHIPS defines 3 different chains for select_sprite_layout, 1 for default, 1 for purchase and 1 for cargos. prepare_layout may benefit from a similar spliting.

[glx22]

Applied #246.