[coop] Check async suspend status in ReqSuspendInitSuspendBlocking case

So the issue is that calling begin_suspend_for_blocking_thread under hybrid
suspend will perform a preemptive suspension of the victim thread.

The preemptive suspend doesn't always succeed.
In particular, thread_state_init_from_sigctx or thread_state_init_from_handle
could return FALSE and into->suspend_can_continue will be set to FALSE.
When the thread_state_init_* functions return FALSE, they also set the
MonoThreadUnwindState:valid to FALSE.

So it is important to check the value of MonoThreadInfo:suspend_can_continue
before proceeding with a suspension.

As a result in suspend_sync in the ReqSuspendInitSuspendRunning case we call
check_async_suspend which checks (for preemptively suspended threads) whethere
suspend_can_continue is true.  If it isn't, we resume the victim thread and
loop once more in suspend_sync_nolock and try again.

We didn't have a check_async_suspend call in the ReqSuspendInitSuspendBlocking
case, so a thread could be considered suspended even if we couldn't capture a
valid MonoThreadUnwindState for it.

That breaks the assertion the call to mono_thread_info_get_last_managed in
async_suspend_critical which needs a valid MonoThreadUnwindState.

Fixes mono#10031

mono/utils/mono-threads.c

@@ -1140,6 +1140,13 @@ suspend_sync (MonoNativeThreadId tid, gboolean interrupt_kernel)
 		if (suspend_result != BeginSuspendOkNoWait)
 			mono_threads_wait_pending_operations ();
 
+		if (!check_async_suspend (info, suspend_result)) {
+			mono_thread_info_core_resume (info);
+			mono_threads_wait_pending_operations ();
+			mono_hazard_pointer_clear (hp, 1);
+			return NULL;
+		}
+
 		// if we tried to preempt the thread already, do nothing.
 		// otherwise (if it's running in blocking mode) try to abort the syscall.
 		if (interrupt_kernel && !did_interrupt)