Add an asset source for ImageDecoder

Bug: 74545298
Test: I6a633553bbb5ff26d84aaf5371b8b43a770afd4f

This allows using ImageDecoder to decode a file in the "assets"
directory of an app.

Change-Id: I2193f052cc2e16c55c7f68f7e51e07cd24ee4df9
2 files changed