Replace newlines with linebreaks when importing without HTML

https://forums.ankiweb.net/t/line-breaks-are-removed-when-importing-csv-on-linux/26451

rslib/src/import_export/text/csv/import.rs

@@ -207,7 +207,7 @@ fn stringify_fn(is_html: bool) -> fn(&str) -> String {
     if is_html {
         ToString::to_string
     } else {
-        htmlescape::encode_minimal
+        |s| htmlescape::encode_minimal(s).replace('\n', "<br>")
     }
 }