[Enhancement] Detect and warn user when `Hashed` is used, `string` is the key, and the new .net randomized hashes are in use

[ndrwrbgs]

Otherwise the cache is only valid for a single execution

[ndrwrbgs]

It appears (not an expert) that AppDomain.CurrentDomain.IsCompatibilitySwitchSet("UseRandomizedStringHashAlgorithm") returns false for net45, net48, etc, netstandard2.0, but null for netcoreapp2.0, so we might be able to call that and check for != false (since it seems null AND/OR false means "off")

[ndrwrbgs]

Alternatively we would implement our own stable hash, but that would be prone to the DoS attacks that prompted .NET to implement randomized hashes at all, hence the suggestion to just 'warn' when they're in use (as some use case may not even INTEND to cache beyond single-process-execution).

[acarteas]

I'm of the opinion that hashes should be stable between runs. I don't think DoS attacks are an appropriate concern in the context of this application. @ndrwrbgs, what's your opinion?

[acarteas]

Versions greater than 3.1.0 now use xxHash, which addresses this issue's concerns.