feat: Case-insensitive search for non-ASCII messages (#5052)

SQLite search with `LIKE` is case-insensitive only for ASCII chars. To make it case-insensitive for
all messages, create a new column `msgs.txt_normalized` defaulting to `NULL` (so we do not bump up
the database size in a migration) and storing lowercased/normalized text there when the row is
created/updated. When doing a search, search over `IFNULL(txt_normalized, txt)`.

src/sql/migrations.rs

@@ -937,6 +937,11 @@ CREATE INDEX msgs_status_updates_index2 ON msgs_status_updates (uid);
             .await?;
     }
 
+    if dbversion < 115 {
+        sql.execute_migration("ALTER TABLE msgs ADD COLUMN txt_normalized TEXT", 115)
+            .await?;
+    }
+
     let new_version = sql
         .get_raw_config_int(VERSION_CFG)
         .await?