Suppress last-ditch download exceptions w/cleanup

Create an encapsulating DownloadException to represent the aggregate
exception set of an ActionResult download. IOExceptions will be retained
through exception suppression, and the outer exception has a property to
indicate if it only represents a sequence of CacheNotFoundExceptions.

InterruptedExceptions interception is improved to cancel pending work
and wrap, through suppression, any DownloadException that also occurred
during the download. InterruptedException being thrown on the download
control thread, it does not require suppression of further interrupts,
and can represent an outer download exception. Thread interrupt status
is suppressed for cancellations, and conveyed on throw.

These exception wrapping efforts allow non-asynchronous frame
representation in stack traces, and much clearer identification of
sources within remote strategy execution which produce failures based on
remote errors.

Any DownloadException in the last-ditch output download under
handleError in RemoteSpawnRunner is added as suppressed to the
initiating exception. Other exceptions (likely local IO) present clear
immediate traces and do not require specialized treatment.

Closes #10029.

PiperOrigin-RevId: 306619678