Make bodypart warmth available in conditions

[mlange-42]

Summary

Interface "Make bodypart warmth available in conditions"

Purpose of change

Be able to make custom bodypart warmth widgets. Required for/used in #59797.

Describe the solution

Make bodypart warmth available as u_val in conditions.

Describe alternatives you've considered

None

Testing

Made a widget using this, in #59797.

Additional context

Usage example:

  {
    "id": "warmth_torso_symbol",
    "type": "widget",
    "style": "symbol",
    "bodypart": "torso",
    "clauses": [
      {
        "id": "scorching",
        "sym": "▲",
        "color": "red",
        "condition": { "compare_int": [ { "u_val": "warmth" }, ">", { "const": 9500 } ] }
      },
      ...
    ]
  }