Super Tiled2Unity 2.4.0 Changes

• Improved feature: Aseprite support no longer depends on Unity's Aseprite Importer (which required Unity 2021.3.15 or newer).
• Improved feature: Now support Aseprite files that have tileset layers.
• Improved feature: All Aseprite blending modes supported.
• Improved support: Can now support Unity 2020.3 and later again.
• New feature: Secondary textures on sprites now supported. (Requires Unity 2022.2 or newer)
• Bug fix: Tileset Atlas now properly supports both V1 and V2 versions of Sprite Packer. Sprite Packer V2 requires Unity version 2021.3 or newer.
• Bug fix: ST2U does not overwrite default texture import settings if a viable preset is available for the texture.