Support dynamic image names / dynamic children for layouts

[KamikotoTkach]

Hi! I am using BetterHud for a skill HUD with many possible ability icons.

Current limitation:

• image.name is resolved statically on config load.
• Conditions can choose between static entries, but image name itself cannot be selected by a placeholder.
• Because of that, a HUD with many ability icons needs hundreds of layout entries, one per icon/state, each with conditions.

Real config impact:

• One skill layout has ~256 image entries.
• Before local optimization it had ~1200 PlaceholderAPI references.
• I moved the logic to native BetterHud placeholders and added tick: 3, but the layout still needs many static entries because the image name cannot be dynamic.

Example of what would help:

images:
  skill_icon:
    name-placeholder: "ability_[cas_hud_key:SWAP_HANDS]_color_sm"
    fallback: "ability_default_color_sm"
    x: -62
    y: -59
    layer: 12