Different API between `tokio::sync::Notify` and `loom::sync::Notify`.

[xuxiaocheng0201]

tokio::sync::Notify has the following methods:

1. pub fn notified(&self) -> Notified<'_>
2. pub fn notify_one(&self)
3. pub fn notify_last(&self)
4. pub fn notify_waiters(&self)

However, loom::sync::Notify only has:

1. pub fn notify(&self)
2. pub fn wait(&self)

The API is different and missing. This makes it difficult to perform some in-place replacements.

[martin-g]

Thanks for reporting this, @xuxiaocheng0201 !
Would you like to send a Pull Request to add the missing methods ?