[Feature request] Add TryRemove(K, out V) overload

[bill-poole]

The TryRemove(K) method implementation retrieves the value associated with the given key, but does not return that value. This means that if we need the value associated with the given key, we need to first invoke TryGet(K, out V) to get the value and then invoke TryRemove(K), which is wasteful.

[bitfaster]

The ItemRemoved event has both key and value - probably not the most convenient but gives you a way to observe removed values without a false lookup that can pollute cache ordering.

This is complicated by the lifetime of IDisposable values. If values are disposable, the cache will auto dispose them on removal. A TryRemove that returns the value would then either need to be a special case, where the caller must dispose the live value returned (which isn't intuitive, and likely one might forget and leak objects), or it would return disposed objects, which may not be valid and may throw if methods are invoked etc. Neither option is great. My rationale here was to do the simplest thing and not expose any potential traps.

The ItemRemoved event fires before disposal, so the value is still alive when the event handler runs. Thus it sidesteps the above.

I suspect caching IDisposable is less common, so it's unfortunate to limit the common case to keep this clean, but that was my tradeoff.

Changing the signature would be a breaking change - I will consider for the next major version, but I'm inclined not to add this.