Implement AImageDecoder dataspace methods

Bug: 135133301
Test: Iffe659e50078139188c3325545624640ae177cc2

Implement AImageDecoderHeaderInfo_getDataSpace, which reports the
default ADataSpace to decode to. It may report ADATASPACE_UNKNOWN, which
means that we've mostly left the colors in their original color profile.
This matches android.graphics.ImageDecoder/BitmapFactory, which would
use a ColorSpace named "Unknown". (It will standardize on DISPLAY_P3 for
some profiles, which again matches the Java classes.)

Implement AImageDecoder_setDataSpace, which allows specifying the
ADataSpace to decode to. It only supports explicit ADataSpaces.

Change-Id: Iba2f9e09531c23fae83ebe13cb9d18394ee3cd59