The versionPreserved instance output filter stream property defaults to false

When getting the properties descriptor of the xwiki+instance output stream, it is a combined descriptor (CompositeFilterStreamDescriptor, named "XWiki instance output stream"), in which you have the following 4 descriptors, in this order:

1. XWiki instance output stream
2. XWiki documents instance output stream (DocumentInstanceOutputProperties)
3. XWiki users instance output stream (UserInstanceOutputProperties)
4. XWiki extensions instance output stream

2 (XWiki documents instance output stream) and 3 (XWiki users instance output stream) both have a "preserve version" (versionPreserved) property. It is set to true by default in "XWiki documents instance output stream" and to false in "XWiki users instance output stream".

The combined properties use the last one.

This is not desirable, because we want to preserve versions by default.

Here are the proposed actions:

• Set versionPreserved to true by default in UserInstanceOutputProperties
• refactor DocumentInstanceOutputProperties and UserInstanceOutputProperties so common properties are grouped in a class they both extend, EntityInstanceOutputProperties.

Note: this is a breaking change.