Rename ImageDecoder.ERRORs

Bug: 73788969
Test: I501e8b76aacd785cb994165ab01dc1b39fea3a1c

Move them into ImageDecoder.DecodeException, which is where they are
actually used. This also provides some more context, so that the prefix
"ERROR_" is no longer necessary, fixing the redundancy/awkwardness in
ERROR_SOURCE_ERROR. Further rename that to SOURCE_MALFORMED_DATA, which
is more descriptive, and does not imply a Java Error.

Change-Id: Ied17ad343650f9c33d9a35b0f9d00ccc22264bd6