message: Add parser improvements to changelog
diff: - Backlinks can be used like lists in expressions including: min, max, sum, avg, count/size, and subqueries
  - Keypath substitution is supported to allow querying over named backlinks and property aliases, see `KeyPathMapping`
  - Parsing backlinks can be disabled at runtime by configuring `KeyPathMapping::set_allow_backlinks`
  + - Support for ANY/SOME/ALL/NONE on list properties (parser only). For example: `ALL items.price > 10`
  + - Support for operator 'IN' on list properties (parser only). For example: `'milk' IN ingredients.name`
  PR [#2989](https://github.com/realm/realm-core/pull/2989).
  -----------
  