PropertyTree memory overuse

[rymsha]

after #10015 was implemented we noticed extreme heap usage increase on some setups.
The consumption is very high for NodeVersion objects, specifically the ones with big amount of KV records in data.

A lot of memory is wasted because each property value is represented by an ArrayList with 1 element - wasting 9 reserved cells (This is how mutable ArrayList works).
Additionally PropertyArray object also wastes a lot of memory - because it uses HashMap. And When there are a bot more than 3000 elements in it 8192 elements are allocated.

[rymsha]

In order to save memory a separate representation of PropertyTree was introduced - specifically for cache.

• PropertyTree is mutable ad must be copied anyway
• PropertyTree is a complex data structure with internal HashMap for quick access by path/key

By storing single KV elements without a List (just a reference to a Value) and storing PropertySets in a List (or just value) we managed to shrink PropertyTree 3.8 MB object into ImputableProperty 1.9 MB object with a greater copy performance as well