Full-text search

[stephencelis]

This PR (draft for now) introduces some potential helpers for SQLite's full-text search capabilities (FTS5). We can refine them further, and potentially quarantine them to a SQLite-only trait/module before merging.

[stephencelis]

Moving this to requiring an FTS5 conformance is technically a breaking change, but it's not valid to call match outside of FTS, so I think it's fine while the library is still 0.x.

[mackoj]

After integrating it into my project, the migration from my custom FTS5 implementation was smooth.

I did encounter two issues:

• inheriting from FTS5, as it conflicted with GRDB’s own FTS5 type. Using @Table(virtual: FTS5.self) would be ideal even though the workaround was simply to prefix it with StructuredQueries.FTS5.

@Table("tokens_fts")
public struct DBTokenFTS: StructuredQueries.FTS5, Codable, Sendable, Hashable {
  @Column(primaryKey: true)
  public let rowid: DBToken.ID
  public let path: String

  public init(rowid: DBToken.ID, path: String) {
    self.rowid = rowid
    self.path = path
  }
}