feat: Support breadcrumb instances deduplication

Description

Deduplicate multiple BreadcrumbGroup instances across the page and render only one inside the respective app layout slot. Only behind appLayoutWidget feature flag, not for production use.

<AppLayout
   breadcrumbs={null}
   content={<>
       <BreadcrumbGroup /> // this one will be rendered in the intended place, even if it did not use the slot
   </>}
/>

See the tests for more details about order resolution and other corner-cases.

Related links, issue #, if available: n/a

How has this been tested?

Added unit and integration tests

Review checklist

_The following items are to be evaluated by the author(s) and the reviewer(s)._ #### Correctness - _Changes include appropriate documentation updates._ - _Changes are backward-compatible if not indicated, see [`CONTRIBUTING.md`](https://github.com/cloudscape-design/components/blob/main/CONTRIBUTING.md#public-apis)._ - _Changes do not include unsupported browser features, see [`CONTRIBUTING.md`](https://github.com/cloudscape-design/components/blob/main/CONTRIBUTING.md#browsers-support)._ - _Changes were manually tested for accessibility, see [accessibility guidelines](https://cloudscape.design/foundation/core-principles/accessibility/)._ #### Security - _If the code handles URLs: all URLs are validated through [the `checkSafeUrl` function](https://github.com/cloudscape-design/components/blob/main/src/internal/utils/check-safe-url.ts)._ #### Testing - _Changes are covered with new/existing unit tests?_ - _Changes are covered with new/existing integration tests?_

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Codecov Report

Attention: Patch coverage is 94.80519% with 4 lines in your changes missing coverage. Please review.

Project coverage is 95.62%. Comparing base (e5fdb4a) to head (8b5a881).

Files	Patch %	Lines
src/app-layout/visual-refresh-toolbar/index.tsx	42.85%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2419 +/- ## ======================================== Coverage 95.62% 95.62% ======================================== Files 720 722 +2 Lines 19163 19237 +74 Branches 6397 6118 -279 ======================================== + Hits 18325 18396 +71 - Misses 784 833 +49 + Partials 54 8 -46 ```

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cloudscape-design / components