devices: vhost-user: GPU features fix and handle tasks like other devices
devices: vhost-user: GPU features fix and handle tasks like other devices

- Spawn detached tasks with an AbortHandle like other devices.

- Bug fix: without calling queue.ack_features at the beginning of
  start_queue, VIRTIO_RING_F_EVENT_IDX causes a hang.

BUG=b:243061269
TEST=presubmit, downstream

Change-Id: I03eba1c60a541cf7862feb434fc9fc1064319629
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3950853
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Commit-Queue: Idan Raiter <39d44ee1f9eb22b80eda08034569d4012456b309@google.com>

google/crosvm,google/crosvm,google/crosvm,google/crosvm