XWIKI-19125: Introduce a displayedAuthor in XWikiDocument

...java/org/xwiki/filter/event/model/WikiDocumentFilter.java

.../java/org/xwiki/filter/xar/internal/XARDocumentModel.java

...iki/filter/xar/internal/output/XAROutputFilterStream.java

...ernal/filter/input/XWikiDocumentLocaleEventGenerator.java

...ernal/filter/output/AbstractEntityOutputFilterStream.java

...rnal/filter/output/XWikiAttachmentOutputFilterStream.java

...ternal/filter/output/XWikiDocumentOutputFilterStream.java

...l/filter/input/AbstractInstanceInputFilterStreamTest.java

.../test/resources/filter/documentwithattachment1content.xml

.../test/resources/filter/documentwithattachment2content.xml

...n/java/org/xwiki/xar/internal/model/XarDocumentModel.java