Add fullbright support for models

[SaintWish]

Could use this ,but it'd probably just be better to wait for the render engine. https://github.com/BlueNightHawk/halflife_fullbright

[tschumann]

Interesting - looks like BlueNightHawk/halflife_fullbright@1794262 works by rendering the model twice - once normally, and then once with each texture overlayed with a blank texture that has a bright white light shone on it.

Incidentally, this is possible with some modifications to studiomdl (tschumann/basis@bc311f7). https://www.the303.org/tutorials/gold_mdl.htm#special shows what it looks like.

[frendship-loost]

Bumping, +1 to tschumann's comment. We already have a variable #define STUDIO_NF_FULLBRIGHT 0x0004 in studio.h. Besides modifying studiomdl (not necessary if using Sven's studiomdl), you would also need to implement this in the studiomodelrenderer.cpp. 2 examples can be found: 1 linked in tschumann's reply above, and 1 in the source of HLAM.

HLAM source line jump to:
https://github.com/SamVanheer/HalfLifeAssetManager/blob/4df74a58a50438b8f4b974e04ab9f24fdfcbb811/src/hlam/formats/studiomodel/StudioModelRenderer.cpp#L855

[SaintWish]

Done with 5ddd33b from going off of BlueNightHawk/halflife_fullbright@1794262#diff-14177a9ffcba74146feb2174098eec9393af0713ba6912ac9957a99fb8ddf516 and FreeSlave/halflife-featureful@3d2af63#diff-38dedf7342576dfb1b4c385b7044cce91868cf96ed837e1e38e5c223b1ed100d