Stream::BlockHostUntilDone now returns Status rather than bool.

The now-deprecated Stream::BlockHostUntilDoneWithStatus remains, to facilitate a
multi-CL renaming transition.  Once all callers have been renamed to
BlockHostUntilDone, *WithStatus will be removed.

The StreamExecutor (private) method has also been renamed to BlockHostUntilDone.
It's only used by Stream.

The StreamExecutorInterface method will be renamed in a separate atomic CL.
It's harder to perform that transition gradually, and we've already performed an
atomic change previously, so we might as well fix it up in one shot.

PiperOrigin-RevId: 178907807