Request: allow to extract Bitmaps from animated GIF/WEBP, including how long each should last

Currently there are still only workarounds for this, but even then, I couldn't find the missing information, of how long each frame I get should last.

Here's one way:
https://medium.com/@bogomazartem/extract-bitmap-frames-from-gif-file-android-9e06d8b709f8

And another, which I'm not sure if it's ok, as it actually plays the animation :

```kt
private fun testWebp() {
val drawable = GlideApp.with(applicationContext).load(R.raw.test_webp).skipMemoryCache(true)
.diskCacheStrategy(DiskCacheStrategy.NONE)
.submit().get() as WebpDrawable
val bitmap = Bitmap.createBitmap(drawable.intrinsicWidth, drawable.intrinsicHeight, Bitmap.Config.ARGB_8888)
val canvas = Canvas(bitmap)
drawable.setBounds(0, 0, bitmap.width, bitmap.height)
drawable.loopCount = 1
val callback = object : CallbackEx() {
override fun invalidateDrawable(who: Drawable) {
val webp = who as WebpDrawable
canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR)
who.draw(canvas)
//image is available here on the bitmap object
Log.d("AppLog", "frameIndex:${webp.frameIndex} frameCount:${webp.frameCount} firstFrame:${webp.firstFrame}")
}
}
drawable.callback = callback
drawable.start()
}
```

And for WEBP (using [this library](https://github.com/zjupure/GlideWebpDecoder/issues/new) with Glide), something similar:

```kt
private fun testGif() {
val drawable = GlideApp.with(applicationContext).load(R.raw.test_gif).skipMemoryCache(true)
.diskCacheStrategy(DiskCacheStrategy.NONE).submit().get() as GifDrawable
val bitmap = Bitmap.createBitmap(drawable.intrinsicWidth, drawable.intrinsicHeight, Bitmap.Config.ARGB_8888)
val canvas = Canvas(bitmap)
drawable.setBounds(0, 0, bitmap.width, bitmap.height)
drawable.setLoopCount(1)
val callback = object : CallbackEx() {
override fun invalidateDrawable(who: Drawable) {
super.invalidateDrawable(who)
val gif = who as GifDrawable
canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR)
who.draw(canvas)
//image is available here on the bitmap object
Log.d("AppLog", "frameIndex:${gif.frameIndex} frameCount:${gif.frameCount} firstFrame:${gif.firstFrame}")
}
}
drawable.callback = callback
drawable.start()
}
```

But there is no official way to do it.
Please offer an official way using Glide, to extract the frames and check how long each frame should last.

I know it's open sourced and technically I could dig the code to find it (I can see it's in ByteBufferGifDecoder, using GifDecoder), but I'd like to request it still.

Please do consider adding this functionality, and if there is one already, please show me a link about this.