CLONE -Backport HHH-5300 to EAP to fix memory leak in QueryPlanCache

An issue with <literal>QueryPlanCache</literal> was discovered that caused a memory leak due to soft references held by the unbound <literal>SoftLimitMRUCache</literal>. The <literal>SoftLimitMRUCache</literal> eventually filled up until a major stop-the-world garbage collection was necessary to clean the <literal>SoftLimitMRUCache</literal> soft references. The solution involves constraining the amount of soft and strong unbound references held in the cache. Entries are evicted using an LRU policy, or by memory pressure from the GC in the case of soft references. Two configuration options are now available, which resolve the issue: hibernate.query.plan_cache_max_strong_references, which defaults to 128 hibernate.query.plan_cache_max_soft_references, which defaults to 2048 Users that want to emulate previous behavior, can set <classname>hibernate.query.plan_cache_max_soft_references</classname> to Integer.MAX_VALUE.