It's possible to get twice the same document entry in Solr when the default locale changes

The entry id in Solr is based on the document default locale, meaning that if you change the default locale, the document id on solr side changes...

Problem is that the code which trigger an index of the document when receiving a document updated event assume the id is a lot more stable (i.e. that the solr index is not nonsense...).

We should ideally fix how Solr is indexed to use the locale (so an empty string) instead of the default locale.