Make ref.listen similar to useEffect

[jeiea]

I probably expected ref.listen would resemble useEffect because I'm familiar with hooks. Anyway I propose this because it appears more convenient.

As far as I understand, currently ref.listen works as follows:

1. It executes the handler synchronously whenever ref.listen is called, if fireImmediately: true.
2. It executes the handler later when the listened provider changes.

I believe it would be more convenient if it operated as follows:

1. Execute handler synchronously when call ref.listen first.
2. Don't execute handler when call ref.listen again (by refresh) in the same provider, and listened provider didn't change.
3. Execute handler later when listened provider changes.

So request for comments.