R1:7c5b5327c8cc

Use stemming in the MySQL fulltext search engine

Summary:
Ref T6740. When we index a document, also save a copy of the stemmed version.

When querying, search the combined corpus for the terms.

(We may need to tune this a bit later since it's possible for literal, quoted terms to match in the stemmed section, but I think this wil rarely cause issues in practice.)

A downside here is that search sort of breaks if you upgrade into this and don't reindex. I wasn't able to find a way to issue the query that…