Upgrade to NH 5.2.0

[fredericDelaporte]

In order to benefit from the CacheBase (nhibernate/nhibernate-core#1777), upgrade to NHibernate 5.2.0.

[fredericDelaporte]

Most caches do no more need an async generation, as their cache implementation do not support async. The inherited default async handling is then suitable for them.

[fredericDelaporte]

For avoiding binary breaking changes, I only see this ugly solution.

Removing a non-virtual method for a virtual inherited one is a breaking change, as some caller may try to call it, as explained here:

Adding virtual to a member
While this change would often work without breaking too many scenarios because C# compiler tends to emit callvirt IL instructions to call non-virtual methods (callvirt performs a null check, while a normal call won't), we can't rely on it. C# is not the only language we target and the C# compiler increasingly tries to optimize callvirt to a normal call whenever the target method is non-virtual and the this is provably not null (such as a method accessed through the ?. null propagation operator). Making a method virtual would mean that consumer code would often end up calling it non-virtually.

And we are in a worst case: we have removed many of these members (all the async ones for all the other caches), counting on virtual inherited ones for replacing them.

Moreover the old void Lock cannot coexist with object Lock in the same class, so we anyway need an "intermediate" class.

[fredericDelaporte]

We do not need it for avoiding a binary breaking change, but it avoids having to rewrite all the XML comments.

[fredericDelaporte]

I intend to merge this soon, in order to allow other pending PR to be done.