Use S3 content-range header to update length of an object during reads

As part of all the openFile work, knowing full length of an object allows for a HEAD to be skipped. But: code knowing only the splits don't know the final length of the file.

If the content-range header is used, then as soon as a single GET is initiated against an object, if the field is returned then we can update the length of the S3A stream to its real/final length

Also: when any input stream fails with an EOF exception, we can distinguish stream-interrupted from "no, too far"