Provide package cache to aldoc when building reference documentation (#2301)

aldoc build was invoked with only --source, so it fell back to its
default package cache ({source}/.alpackages) which does not exist for
artifact-based apps. As a result every reference to another module was
reported as 'Referenced module not loaded' and the corresponding links
in the generated documentation were left unresolved.

Populate a package cache with all apps and their dependencies (the
latter were already downloaded and computed by CalculateProjectsAndApps
but never used) and pass it to aldoc via --packagecache so cross-module
references resolve.

Fixes #2302 

### ✅ Checklist

- [x] Add tests (E2E, unit tests)
- [x] Update RELEASENOTES.md
- [ ] Update documentation (e.g. for new settings or scenarios)
- [ ] Add telemetry

<!-- Include more checklist entries, if needed -->

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Co-authored-by: spetersenms <spetersenms@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>