Merge remote-tracking branch 'remotes/marcandre/tags/clip-pull-request' into staging

Merge remote-tracking branch 'remotes/marcandre/tags/clip-pull-request' into staging

# gpg: Signature made Tue 31 Aug 2021 14:29:27 BST
# gpg:                using RSA key 87A9BD933F87C606D276F62DDAE8E10975969CE5
# gpg:                issuer "marcandre.lureau@redhat.com"
# gpg: Good signature from "Marc-André Lureau <marcandre.lureau@redhat.com>" [full]
# gpg:                 aka "Marc-André Lureau <marcandre.lureau@gmail.com>" [full]
# Primary key fingerprint: 87A9 BD93 3F87 C606 D276  F62D DAE8 E109 7596 9CE5

* remotes/marcandre/tags/clip-pull-request:
  ui/vdagent: add a migration blocker
  ui/gtk-clipboard: emit release clipboard events
  ui/vdagent: send release when no clipboard owner
  ui/gtk-clipboard: use qemu_clipboard_info helper
  ui/vdagent: send empty clipboard when unhandled
  ui/vdagent: use qemu_clipboard_info helper
  ui/vdagent: use qemu_clipboard_peer_release helper
  ui/vdagent: split clipboard recv message handling
  ui/vdagent: reset outbuf on disconnect
  ui/vdagent: disconnect handlers and reset state on finalize
  ui/clipboard: release owned grabs on unregister
  ui/clipboard: add qemu_clipboard_peer_release() helper
  ui/clipboard: add qemu_clipboard_peer_owns() helper
  ui/clipboard: add helper to retrieve current clipboard
  ui/gtk-clipboard: fix clipboard enum typo
  ui/gtk-clipboard: use existing macros
  ui/vdagent: remove copy-pasta comment
  ui/vdagent: fix leak on error path

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>