[gc] Fix crash when doing WaitForPendingFinalizers

[gc] Fix crash when doing WaitForPendingFinalizers

The crash would come from a use-after-free of stack memory: in coop_cond_timedwait_alertable, we would allocate the struct we pass to the mono_thread_info_install_interrupt function on the stack. But there is no guarantee as to when break_coop_alertable_wait is run. The fix is to allocate the data passed to mono_thread_info_install_interrupt on the heap, and free it in the callback, or if it hasn't been interrupted.