- Move identifier detection to `Zotero.Utilities.Internal.extractIdentifiers()`
so that it can be used for things other than Add Item by Identifier
(e.g., translation-server)
- Add a `Zotero.Translate.Search::setIdentifier()` function that takes an
identifier object produced by `extractIdentifiers()` (`{ DOI: "10/..." }`),
converts that to the search format expected by translators, and calls setSearch()