Add support for migrating ac:emoticon tags

When adding emoticons in Confluence pages, the emotes are stored in the storage format as something similar to the following :

<ac:emoticon ac:name="cross" ac:emoji-shortname=":cross_mark:" ac:emoji-id="atlassian-cross_mark" ac:emoji-fallback=":cross_mark:" />

The goal of this issue is to add support for the ac:emoticon tag migration in XWiki.

The following export contains a page with just two emotes, for testing purposes : Confluence-export-space-~722966791.zip