[WIP] Sprays Importer/Gallery + fixed empty spray + NeoUI Texture/Image button + stb libraries

[nullsystem]

Description

TODO:

• Try out exporting DXT5 instead of DXT1. Seems DXT5 works for spray and can deal with transparency well
• Change importer behavior from always the same spray.vtf to also applying by filename's basename + .vtf/.vmt
• Change settings apply behavior to be more like the others settings?

• Spray now put into the NeoUI settings menu
  • Import button to import sprays
  • Gallery button to pick a spray from current already available set
  • An image on the left to show the current spray
  • Outputs VTF 7.4 DXT1/DXT5 format and 2 VMT files, one for UI and one general
• Spray fix - fixed for local player's spray not showing up properly
  • The issue affected both default and custom sprays
• Function to generate VTF 7.4 + DXT1/DXT5 image
  • This is partially because Source SDK's RGBA8888 to DXT conversion was broken, so a "custom" function is done instead
  • It just lays out the VTF headers, the 4 mipmaps from smallest to largest, then DXT1 or DXT5 block per mipmap images
  • It will use DXT5 if there's any transparency/usage of alpha values, otherwise DXT1 will be use if no alpha is needed due to the smaller size
• NeoUI image/texture support - New Texture and ButtonTexture
  • The texture can be initialized from vmt texture, vtf texture direct, and general images like PNG or JPG
  • Makes sure image aspect ratio and fit is correct within the given bounds
• NeoUI scrolling fixes
  • Fixed to use y-partition instead of widget indexes
  • Scrollbar is now determined by X-margin
• New libraries usages:
  • All from: https://github.com/nothings/stb
  • stb_image.h for image reading (PNG, JPG) (used for both spray importer and NeoUI image support)
  • stb_image_resize2.h for image resizing (used for spray importer)
  • stb_dxt.h for outputting DXT1 blocks (used for spray importer)

Toolchain

• Linux GCC Distro Native Arch/GCC 14

Linked Issues

• fixes [FEATURE] Root NeoUI - Sprays #602