SoftCleanable and WeakCleanable

[Florian Weimer]

* Alan Bateman:

> On 01/08/2020 10:23, Florian Weimer wrote:
>> Are jdk.internal.ref.SoftCleanable and jdk.internal.ref.WeakCleanable
>> actually used?
>>
>> CleanerTest rests them, but I don't see any other mentions of these
>> classes.

> Do you mean used outside of the cleaner implementation? Maybe you are 
> looking to change them to non-public?

It's not clear to me how the cleaner implementation itself uses them.
java.lang.ref.Cleaner only needs PhantomCleanableRef.