XWIKI-10247: Impossible to use a rendering syntax installed as extension

(cherry picked from commit 5af363a5e168fd322963ac3c7004a034f25a993a)

Conflicts:
	xwiki-platform-core/xwiki-platform-rendering/xwiki-platform-rendering-xwiki/src/main/java/org/xwiki/rendering/internal/parser/DefaultContentParser.java
XWIKI-10246: Whatever happen when saving backlinks it should never break the document save

(cherry picked from commit 99cea5a6742ae080af6ed267800fe3c1df61f8bf)