Responsive border classes

Hi!

I'm trying to enable responsive classes for borders as described [here](https://getbootstrap.com/docs/5.1/utilities/api/#enable-responsive). But when I add the code (see below) after importing the bootstrap5 theme, it gets ignored. If I import bootstrap-utlities first, add the code and after that import the theme, I get the responsive classes but lose some settings (e.g. negative margins)... Does anyone have an idea how to realize this?

```
$utilities: map-merge(
$utilities,
(
"border": map-merge(
map-get($utilities, "border"),
( responsive: true ),
),
"border-top": map-merge(
map-get($utilities, "border-top"),
( responsive: true ),
),
"border-end": map-merge(
map-get($utilities, "border-end"),
( responsive: true ),
),
"border-bottom": map-merge(
map-get($utilities, "border-bottom"),
( responsive: true ),
),
"border-start": map-merge(
map-get($utilities, "border-start"),
( responsive: true ),
),
)
);
```

Start with the Bootstrap 5.1 utilities API linked in the issue, then inspect the provided Sass configuration and its import order. Confirm which import preserves the theme settings while enabling responsive border classes; done means responsive border utilities work without losing options such as negative margins.

Written by the indexing model from the issue text.