Installers should be able to inherit and merge dependencies from package

Description of the new feature / enhancement

This is an excerpt from a package I am about to submit - as you can see, 2 out of 3 dependencies are the same for both installers:

PackageIdentifier: OpenBoxLab.RaiDrive
PackageVersion: 2023.9.32
# ...
Installers:
  - InstallerUrl: https://app.raidrive.com/d86ea6fa40f74010914976063f94774b/release/stable/RaiDrive_2023.9.32_x64.msi
    Architecture: x64
    InstallerSha256: B486683E0C223A1FF7D0251A050DF80A649D09F47F7026A5197D79F1E11281A5
    Dependencies:
      PackageDependencies:
        - PackageIdentifier: Microsoft.DotNet.DesktopRuntime.6
        - PackageIdentifier: Microsoft.EdgeWebView2Runtime
        - PackageIdentifier: Microsoft.VCRedist.2015+.x64
  - InstallerUrl: https://app.raidrive.com/d86ea6fa40f74010914976063f94774b/release/stable/RaiDrive_2023.9.32_x86.msi
    Architecture: x86
    InstallerSha256: 32D174DDF313150E125BB020DC9CC79CDF5EF5C7D4842E831A7F65B970004F95
    Dependencies:
      PackageDependencies:
        - PackageIdentifier: Microsoft.DotNet.DesktopRuntime.6
        - PackageIdentifier: Microsoft.EdgeWebView2Runtime
        - PackageIdentifier: Microsoft.VCRedist.2015+.x86
ManifestType: installer
ManifestVersion: 1.5.0

It seems sensible to refactor to:

PackageIdentifier: OpenBoxLab.RaiDrive
PackageVersion: 2023.9.32
# ...
Dependencies:
  PackageDependencies:
    - PackageIdentifier: Microsoft.DotNet.DesktopRuntime.6
    - PackageIdentifier: Microsoft.EdgeWebView2Runtime
Installers:
  - InstallerUrl: https://app.raidrive.com/d86ea6fa40f74010914976063f94774b/release/stable/RaiDrive_2023.9.32_x64.msi
    Architecture: x64
    InstallerSha256: B486683E0C223A1FF7D0251A050DF80A649D09F47F7026A5197D79F1E11281A5
    Dependencies:
      PackageDependencies:
        - PackageIdentifier: Microsoft.VCRedist.2015+.x64
  - InstallerUrl: https://app.raidrive.com/d86ea6fa40f74010914976063f94774b/release/stable/RaiDrive_2023.9.32_x86.msi
    Architecture: x86
    InstallerSha256: 32D174DDF313150E125BB020DC9CC79CDF5EF5C7D4842E831A7F65B970004F95
    Dependencies:
      PackageDependencies:
        - PackageIdentifier: Microsoft.VCRedist.2015+.x86
ManifestType: installer
ManifestVersion: 1.5.0

Surprisingly, this doesn't work, as the installers' dependencies (or at least the package dependencies) will be overridden. I would have found it more intuitive if they would have been inherited and merged by default, but for the sake of backwards compatibility, I'd suggest a boolean option inherit:

PackageIdentifier: OpenBoxLab.RaiDrive
PackageVersion: 2023.9.32
# ...
Dependencies:
  PackageDependencies:
    - PackageIdentifier: Microsoft.DotNet.DesktopRuntime.6
    - PackageIdentifier: Microsoft.EdgeWebView2Runtime
Installers:
  - InstallerUrl: https://app.raidrive.com/d86ea6fa40f74010914976063f94774b/release/stable/RaiDrive_2023.9.32_x64.msi
    Architecture: x64
    InstallerSha256: B486683E0C223A1FF7D0251A050DF80A649D09F47F7026A5197D79F1E11281A5
    Dependencies:
      Inherit: true
      PackageDependencies:
        - PackageIdentifier: Microsoft.VCRedist.2015+.x64
  - InstallerUrl: https://app.raidrive.com/d86ea6fa40f74010914976063f94774b/release/stable/RaiDrive_2023.9.32_x86.msi
    Architecture: x86
    InstallerSha256: 32D174DDF313150E125BB020DC9CC79CDF5EF5C7D4842E831A7F65B970004F95
    Dependencies:
      Inherit: true
      PackageDependencies:
        - PackageIdentifier: Microsoft.VCRedist.2015+.x86
ManifestType: installer
ManifestVersion: 1.5.0

Since most of the time that this feature would be handy is probably within the context of architecture-specific packages, it may become obsolete if #1665 got implemented. I imagine then we could write someting like this:

PackageIdentifier: OpenBoxLab.RaiDrive
PackageVersion: 2023.9.32
# ...
Dependencies:
  PackageDependencies:
    - PackageIdentifier: Microsoft.DotNet.DesktopRuntime.6
    - PackageIdentifier: Microsoft.EdgeWebView2Runtime
    - PackageIdentifier: Microsoft.VCRedist.2015+.{$architecture}
Installers:
  - InstallerUrl: https://app.raidrive.com/d86ea6fa40f74010914976063f94774b/release/stable/RaiDrive_2023.9.32_x64.msi
    Architecture: x64
    InstallerSha256: B486683E0C223A1FF7D0251A050DF80A649D09F47F7026A5197D79F1E11281A5
  - InstallerUrl: https://app.raidrive.com/d86ea6fa40f74010914976063f94774b/release/stable/RaiDrive_2023.9.32_x86.msi
    Architecture: x86
    InstallerSha256: 32D174DDF313150E125BB020DC9CC79CDF5EF5C7D4842E831A7F65B970004F95
ManifestType: installer
ManifestVersion: 1.5.0

Proposed technical implementation details

No response

No files, tests, or entry points are named. Start by reviewing how package-level and installer-level Dependencies are represented and merged, then compare the proposed inheritance behavior with the possible architecture-specific approach in issue #1665. Done means an agreed, backward-compatible dependency inheritance design with validation coverage.