As a first iteration we can implement a the config fallback to autogenerate the backlink markers.
There's already some work done in proof of concept patches. We can probably extract some stuff from there. See https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Cite/+/1082440 and the relation chain there.
Implementation details:
- The autogeneration will use a list of characters
- We need a feature flag to allow transition between the current defaults and i18n messages
- The general default for the new system will be an a-z Alphabet
- With MediaWiki-extensions-CLDR the default is the ContentLanguage
- It should be possible to change that default using wgCiteDefaultBacklinkAlphabet
- Should be backwards compatible with the current mechanism where a i18n message is used
- Add tests