io: Add qio_channel_wait_cond() helper

Add the helper to wait for QIO channel's IO availability in any
context (coroutine, or non-coroutine).  Use it tree-wide for three
occurences.

Cc: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Link: https://lore.kernel.org/r/20251022192612.2737648-2-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>

include/io/channel.h

@@ -871,6 +871,21 @@ void qio_channel_wake_read(QIOChannel *ioc);
 void qio_channel_wait(QIOChannel *ioc,
                       GIOCondition condition);
 
+/**
+ * qio_channel_wait_cond:
+ * @ioc: the channel object
+ * @condition: the I/O condition to wait for
+ *
+ * Block execution from the current thread until
+ * the condition indicated by @condition becomes
+ * available.
+ *
+ * This will work with/without a coroutine context, by automatically select
+ * the proper API to wait.
+ */
+void qio_channel_wait_cond(QIOChannel *ioc,
+                           GIOCondition condition);
+
 /**
  * qio_channel_set_aio_fd_handler:
  * @ioc: the channel object