Support splicing manifests from multiple Cargo workspaces #3934

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@malt3

The following contributors were found for this pull request:

✅ 275962d Author: @malt3 <m***l@apple.com>
✅ 4d11c0b Author: @criemen <co*****us@github.com>
✅ 275962d Co-Author: @stevebarrau <98589981+stevebarrau@users.noreply.github.com>

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