Add support for unshaded displacement maps

[ruddygreat]

About the PR

Made a couple tiny changes to DisplacementMapSystem & DisplacementData to allow displacements to propely be applied to unshaded layers on a sprite.

Why / Balance

It's a small thing that's been annoying the artists on the fork I play on + it seems a few people have been talking about it in the main wizden discord.

Technical details

Added the DisplacedStencilDrawUnshaded shader, a copy of DisplacedStencilDraw with light_mode set to unshaded.
Added the ShaderOverrideUnshded field to DisplacementData that points to the new shader.
Added a check to DisplacementMapSystem to use the new shader if the original layer was unshaded.

To use it, all you need to do is specify an unshaded layer in the clothingComponent, like so

  - type: Clothing
    sprite: Clothing/Head/Hats/beret_engineering.rsi
    clothingVisuals:
      head:
      - state: equipped-HELMET
        shader: unshaded

Media

old (left) & new (right), using the above example clothing comp

Requirements

• I have read and am following the Pull Request and Changelog Guidelines.
• I have added media to this PR or it does not require an ingame showcase.

Changelog

no CL; not player-facing enough?

[TheShuEd]

Looks fine! Can you please attach to PR description a YML example of using this new feature?

[ruddygreat]

Looks fine! Can you please attach to PR description a YML example of using this new feature?

Example added! Also changed the example screenshot to something more obvious.