- If we have some value `X` in the cache, and we put `X` a second time
into the same location, `X` shouldn't be cleaned up because it wasn't
actually removed from the cache.
- With this feature, it's necessary to implement `put` in terms of
`backingMap.compute`, because we need to compare the old and the new
value atomically, and based on that, decide whether to create a new
soft reference.
^KT-61222
Marco Pennekamp
53e545aa3f