Some meshes return false from `CanApplySnowShader()` when they should be true

[hakasapl]

For example, consider the FORM ID 0401F9E4 from Dragonborn. This is swapped for a tundra rock in whiterun because the conditional model::must_only_contain_textureset(stat, { "Snow", "Mask" }) passes. This static does not have any snow material so the only way it would be considered for swap is if the above passes. It has a snow texture as an alternate texture, however, it does not have any snow material nor snowy mountain alternate textures for the mountains themselves.

Then, during CanApplySnowShader() that static returns SWAP_RESULT::kBaseFail because the base object (const auto base = util::get_original_base(a_ref)) does not equal static, because it was swapped and assumed to already be snowy.

Fixes include:

• Create a better snowy version in SnowOverSkyrim.esp
• Removing the base != a_static check in CanApplySnowShader(), though I'm not sure of the implications of doing that
• More comprehensive lookup in get_snow_variants to account for cases like this - I have not given that much thought yet

Let me know what you think

[powerof3]

It's been a while so I don't really remember the whole snow swap generation system, but yeah it could use a rework. The automated form swap was always meant to be proof of concept so it was good enough.

I'll wait for any more PRs? before trying something out.

[hakasapl]

@powerof3 I'm all set for now, with that last PR things seem to be working great with PBR