Document remote clone events, and QThreadOptions packet

This commit documents in both manual and NEWS:

 - the new remote clone event stop reply,
 - the new QThreadOptions packet and its current defined options,
 - the associated "set/show remote thread-events-packet" command,
 - and the associated QThreadOptions qSupported feature.

Approved-By: Eli Zaretskii <eliz@gnu.org>
Change-Id: Ic1c8de1fefba95729bbd242969284265de42427e