I thought this was going to be a blogpost for native support or a fancy workaround. Instead it's similar to Algolia's solution which is just sending all of your data to their servers as well as Google's.
OP here. You're right the solution is based on the existing documented full text search solutions. You can technically only sent the data you need indexed and the ID instead of sending all data. There is no native mechanism and firebase functions makes it as seamless as possible.