Allow multitile sprites to be animated

[Fris0uman]

Summary

Interface "Allow multitile sprites to be animated"

Purpose of change

Allow multitile sprites to be animated

Describe the solution

Piggy back on #50180 that made multitile accept variants and use those variants for animation

Describe alternatives you've considered

Load animated bool for subsprites too

Testing

Using this json for t_soil

{
  "id": "t_soil",
  "fg": 4169,
  "multitile": true,
  "additional_tiles": [
    { "id": "center", "fg": 4147 },
    {
      "id": "corner",
      "animated": true,
      "fg": [
        { "weight": 2, "sprite": [ 4149, 4152, 4150, 4148 ] },
        { "weight": 1, "sprite": [ 4149, 4153, 4150, 4148 ] },
        { "weight": 1, "sprite": [ 4149, 4152, 4151, 4148 ] }
      ]
    },
    {
      "id": "t_connection",
      "animated": true,
      "fg": [ { "weight": 2, "sprite": [ 4165, 4168, 4166, 4164 ] }, { "weight": 1, "sprite": [ 4165, 4168, 4167, 4164 ] } ]
    },
    {
      "id": "edge",
      "animated": true,
      "fg": [ { "weight": 2, "sprite": [ 4156, 4154 ] }, { "weight": 1, "sprite": [ 4156, 4155 ] } ]
    },
    {
      "id": "end_piece",
      "animated": true,
      "fg": [
        { "weight": 2, "sprite": [ 4159, 4162, 4160, 4157 ] },
        { "weight": 1, "sprite": [ 4159, 4163, 4160, 4157 ] },
        { "weight": 1, "sprite": [ 4159, 4162, 4161, 4157 ] },
        { "weight": 1, "sprite": [ 4159, 4162, 4160, 4158 ] }
      ]
    },
    { "id": "unconnected", "fg": [ 4169, 4169 ] }
  ]
}

2021-08-31.11-31-30.mp4

Additional context

[dseguin]

I just tried this out. It's really cool!

[I-am-Erk]

Would it be difficult to add an attribute like:

  "id": "t_soil",
  "fg": 4169,
  "multitile": true,
  "sync_animations": true

Default false, and if false, the animation for each tile would start on a random frame?

EDIT: i just realized how small this PR is. My change could be a follow up feature.

[int-ua]

Looks like it's not backward-compatible as in tilesets that add these new attributes will be causing errors on stable builds.

[Fris0uman]

Ah right, because the animated field is not loaded for subtiles in previous version and unvisited fields cause error