Preserve WinRT async error details in LocalBundleReader

[Copilot]

Description

Fixes a targeted review issue in LocalBundleReader::LoadBundleAsync: WinRT async failures were being converted to std::runtime_error, which can collapse diagnostics when surfaced through IAsyncOperation::get().

Type of Change

Erase all that don't apply.

• Bug fix (non-breaking change which fixes an issue)

Why

LoadBundleAsync runs in a WinRT coroutine (IAsyncOperation<IBuffer>). Converting winrt::hresult_error to std::runtime_error in this path risks losing original WinRT error metadata/message at the async boundary.

What

• Exception propagation
  • Replace std::runtime_error conversion with direct rethrow of the original WinRT exception.
• Scope
  • Single-file, single-path change in /vnext/Microsoft.ReactNative/Utils/LocalBundleReader.cpp.
  • No behavioral changes outside async error propagation semantics.

catch (winrt::hresult_error const &) {
  throw;
}

Screenshots

N/A

Testing

No new tests were added for this scoped exception-handling adjustment.

Changelog

Should this change be included in the release notes: no

Preserve detailed WinRT async error information in LocalBundleReader::LoadBundleAsync by avoiding conversion to std::runtime_error.