Remove GC Compaction trigger

[muratg]

@KKhurin @davidfowl

Looks like we may have room for improvement here.

[muratg]

@KKhurin Are you able to help us with this?

[KKhurin]

Let's have a discussion.

[DamianEdwards]

I just hit what I think is a down side of the current implementation in that it appears we purge the cache on every Gen2 collection, which in my case was occurring during app start as I was forcibly priming my cache.

[JunTaoLuo]

Currently compaction is triggered by a gen2 collection by the GC. This is not the best trigger since it may occur frequently and does not correlate to the actual memory usage of the cache.

The proposal is to remove the current trigger and instead rely on the user or external triggers to decide when to compact the cache. This will require us to expose the Compact on the interface. Note that there's currently no way of accurately determining the memory usage by the cache so it's difficult to figure out if or how much compaction should occur.