Improve xrui textures

[speigg]

Summary

Improve XRUI textures + expose more encode options

A lot more configuration settings have been exposed. We should use them appropriately:

export enum UASTCFlags {
  /** Fastest is the lowest quality, although it's stil substantially higher quality vs. BC1/ETC1. It supports 5 modes.
		/* The output may be somewhat blocky because this setting doesn't support 2/3-subset UASTC modes, but it should be less blocky vs. BC1/ETC1.
		/* This setting doesn't write BC1 hints, so BC1 transcoding will be slower. 
		/* Transcoded ETC1 quality will be lower because it only considers 2 hints out of 32.
		/* Avg. 43.45 dB
     */
  UASTCLevelFastest = 0,

  /** Faster is ~3x slower than fastest. It supports 9 modes.
		/* Avg. 46.49 dB
		*/
  UASTCLevelFaster = 1,

  /** Default is ~5.5x slower than fastest. It supports 14 modes.
		/* Avg. 47.47 dB
		*/
  UASTCLevelDefault = 2,

  /** Slower is ~14.5x slower than fastest. It supports all 18 modes.
		/* Avg. 48.01 dB
		*/
  UASTCLevelSlower = 3,

  /** VerySlow is ~200x slower than fastest. 
		/* The best quality the codec is capable of, but you'll need to be patient or have a lot of cores.
		/* Avg. 48.24 dB
		*/
  UASTCLevelVerySlow = 4,

  UASTCLevelMask = 0xf,

  /** By default the encoder tries to strike a balance between UASTC and transcoded BC7 quality.
		/** These flags allow you to favor only optimizing for lowest UASTC error, or lowest BC7 error.
		*/
  UASTCFavorUASTCError = 8,
  UASTCFavorBC7Error = 16,

  UASTCETC1FasterHints = 64,
  UASTCETC1FastestHints = 128,
  UASTCETC1DisableFlipAndIndividual = 256,

  /**
   * Favor UASTC modes 0 and 10 more than the others (this is experimental, it's useful for RDO compression)
   */
  UASTCFavorSimplerModes = 512
}
export interface KTX2EncodeOptions {
  /**
   * If true, the input is assumed to be in sRGB space. Be sure to set this correctly! (Examples: True on photos, albedo/spec maps, and false on normal maps.)
   * @default false
   */
  srgb?: boolean
  /**
   * Sets the ETC1S encoder's quality level, which controls the file size vs. quality tradeoff
   * Range is [1,256]
   * @default 128
   */
  qualityLevel?: number
  /**
   * The compression_level parameter controls the encoder perf vs. file size tradeoff for ETC1S files
   * It does not directly control file size vs. quality - see qualityLevel
   * Range is [0,6]
   * @default 2
   */
  compressionLevel?: number
  /**
   * If true, the encoder will output a UASTC texture, otherwise a ETC1S texture.
   * @default false
   */
  uastc?: boolean
  /**
   * Use UASTC Zstandard supercompression. Use with uastc = true
   * @default false
   */
  uastcZstandard?: boolean
  /**
   * Sets the UASTC encoding performance vs. quality tradeoff, and other lesser used UASTC encoder flags.
   * This is a combination of flags. See UASTCFlags
   */
  uastcFlags?: number
  /**
   * Tunes several codec parameters so compression works better on normal maps.
   * @default false
   */
  normalMap?: boolean
  /**
   * If true, the encoder will generate mipmaps.
   * @default false
   */
  mipmaps?: boolean
  /**
   * If true the source images will be Y flipped before compression
   * @default false
   */
  yFlip?: boolean
}

For fast encoding of XRUI compressed textures, these settings are appropriate:

{
        srgb: true,
        uastc: true,
        uastcFlags: UASTCFlags.UASTCLevelFastest
}

or

{
        srgb: true,
        compressionLevel: 0,
        qualityLevel: 256
}

For exporting ktx2 files, higher compressionLevel should be used.