Consider adding workaround for U + gainmap + hardware bitmap bug

[jreck]

Prior to Android V there exists a bug where when:

1. A decode to Config.HARDWARE is requested
2. The image format is A8 / gray8
3. The device supports A8 hardware buffers
4. The device is using OpenGL

Then the decode fails. As A8 images are extremely rare, this hadn't come up before. However, with the addition of gainmap images the usage of A8 "images" became much more common as a common space/quality tradeoff for the gainmap is to use a8 and provide only luminance modulation as a result. In this scenario it becomes quite possible for all 4 of the above conditions to be hit.

However, it is rather easy to both detect the presence of the bug (simply try to copy an A8 bitmap to Config.HARDWARE - if null is returned the bug is present) and to workaround it in a decently efficient means by simply decoding to non-hardware first, converting the A8 gainmap to 8888, and then copying the result to HARDWARE and returning that. This is not dissimilar to how decoding directly to HARDWARE works, so performance impact should be minimal. See the Glide implementation of both here: bumptech/glide#5357

If nothing is done about this then the failure mode is simply that the decoding of the gainmap portion fails, but the primary image is still successfully returned. As in, the behavior simply matches what Android T did, prior to the introduction of gainmaps. So the failure mode is quite forgiving.

[jreck]

To reproduce decode this: https://cs.android.com/android/platform/superproject/main/+/main:frameworks/base/tests/graphics/SilkFX/assets/gainmaps/fountain_night.jpg

to a Config.HARDWARE output and check that bitmap#getGainmap() returns non-null. You can force this failure path on a pixel device by first doing adb shell setprop debug.hwui.renderer skiagl (kill & re-launch the app to pick up the setting change)

[jreck]

Correction to #1, you can't simply .copy the Config.ALPHA_8 to Config.ARGB_8888, you need to instead do this:

private static Bitmap copyWithOpaqueAlpha(Bitmap bitmap) {
  Bitmap newContents =
      Bitmap.createBitmap(
          bitmap.getWidth(), bitmap.getHeight(), Config.ARGB_8888);
  Canvas canvas = new Canvas(newContents);
  Paint paint = new Paint();
  paint.setColorFilter(
      new ColorMatrixColorFilter(
          new float[] {
            0f, 0f, 0f, 1f, 0f,
            0f, 0f, 0f, 1f, 0f,
            0f, 0f, 0f, 1f, 0f,
            0f, 0f, 0f, 0f, 255f
          }));
  canvas.drawBitmap(bitmap, 0f, 0f, paint);
  canvas.setBitmap(null);
  return newContents;
}

to transform the alpha into rgbx