Use ImageDecoder for BitmapDrawable

If required due to density mismatches the ImageDecoder will not
upscale the image at decode time, but instead will decode at the
bitmaps default size and upscale at draw time.  This can be a
significant memory savings for low-dpi assets being used on a high-dpi
device.

However, if the provided asset has a higher dpi level than the bitmaps
default density then we will match BitmapFactories behavior and downscale
the bitmap to match the default density.

Bug: 63909536
Test: CtsGraphicsTestCases
Change-Id: I189306b7a3b706bed32bb267970ade27a57c0e7f