XWIKI-10252: Add and/or edit objects in a page

* Provide a new object policy to edit but also create new objects in on step
XWIKI-10252: Add and/or edit objects in a page

* Avoid a NullPointerException
XWIKI-10252: Add and/or edit objects in a page

* Add some predefined string identifiers

Conflicts:
	xwiki-platform-core/xwiki-platform-oldcore/src/main/java/com/xpn/xwiki/doc/XWikiDocument.java
XWIKI-10252: Add and/or edit objects in a page

* Remove an empty comment
XWIKI-10252: Add and/or edit objects in a page

* Make the object policy keywords 'final'
XWIKI-10252: Add and/or edit objects in a page

* Rename variables for lisibility
XWIKI-10252: Add and/or edit objects in a page

* Change the name of the default policy (the one of the old core)
XWIKI-10252: Add and/or edit objects in a page

* Change the parsing of parameters using regular expressions
XWIKI-10252: Add and/or edit objects in a page

* Avoid 2 look-ups of the same information
XWIKI-10252: Add and/or edit objects in a page

* Use `entrySet()` loops instead of `keySet()` loops.
* Use a document resolver to find references
XWIKI-10252: Add and/or edit objects in a page

* Remove another 2-lookups in a same object
XWIKI-10252: Add and/or edit objects in a page

* Add an ObjectPolicyType enum type
XWIKI-10252: Add and/or edit objects in a page

* Change the structure using a SortedMap instead of a List
XWIKI-10252: Add and/or edit objects in a page

* Fix a problem when string input is `null`
XWIKI-10252: Add and/or edit objects in a page

* Update the pull request to 6.2 version