XWIKI-11480: Wrong previous syntax when merging a document with EM
XWIKI-10818: Wrong syntax when importing very old document (that does not explicitely containg the syntax)

(cherry picked from commit a250d09df676c70972742c17e15307d1c0b2d71f)

Conflicts:
	xwiki-platform-core/xwiki-platform-wikistream/xwiki-platform-wikistream-streams/xwiki-platform-wikistream-stream-xar/src/main/java/org/xwiki/wikistream/xar/internal/input/DocumentLocaleReader.java

(cherry picked from commit 66fc5768a14d970ad81ecf430cb58281d881bf28)
(cherry picked from commit 4012902fe38c0147ecb20885e542a94c36debd9b)

Conflicts:
	xwiki-platform-core/xwiki-platform-wikistream/xwiki-platform-wikistream-streams/xwiki-platform-wikistream-stream-xar/src/test/resources/xar/xar1.input.test