winget doesn't automatically understand machine-scope MSI installers

Description of the new feature / enhancement

When a winget manifest contains both a user and a machine scope installer definition, both MSIs, winget-cli on the client side doesn't automatically handle the machine-scope case for MSIs (aka appending ALLUSERS=1 on the commandline).

winget-cli should automatically understand machine-scope MSI installs wihtout the package-maintainers having to manually define installer switches. This already works for user-scope MSI (appending /qb, /qn etc., and wix, inno installers etc.).

Proposed technical implementation details

Given an installer manifest excerpt like this:

Installers:
- Architecture: x64
  InstallerType: msi
  Scope: user
  InstallerUrl: https://github.com/pdfarranger/pdfarranger/releases/download/1.10.0/pdfarranger-1.10.0-windows-installer.msi
  InstallerSha256: B77A5DC7C956F1E0986664B0587B9B7532CA304590F4F1C86B03960486DDE4F6
- Architecture: x64
  InstallerType: msi
  Scope: machine
  InstallerUrl: https://github.com/pdfarranger/pdfarranger/releases/download/1.10.0/pdfarranger-1.10.0-windows-installer.msi
  InstallerSha256: B77A5DC7C956F1E0986664B0587B9B7532CA304590F4F1C86B03960486DDE4F6

which is an edited version of https://github.com/microsoft/winget-pkgs/blob/master/manifests/p/PDFArranger/PDFArranger/1.10.0/PDFArranger.PDFArranger.installer.yaml to add support for machine-scope installs, winget-cli should install the MSI properly for all users because "Scope: machine" was defined in the manifest.

Currently, this is not the case. winget-cli does not append the correct parameter (ALLUSERS=1) and the machine-scope installer ends up being installed per-user anyway, despite winget install --scope machine.

A workaround I tested is to manually specify the ALLUSERS=1 switch. This works:

Installers:
- Architecture: x64
  InstallerType: msi
  Scope: user
  InstallerUrl: https://github.com/pdfarranger/pdfarranger/releases/download/1.10.0/pdfarranger-1.10.0-windows-installer.msi
  InstallerSha256: B77A5DC7C956F1E0986664B0587B9B7532CA304590F4F1C86B03960486DDE4F6
- Architecture: x64
  InstallerType: msi
  Scope: machine
  InstallerUrl: https://github.com/pdfarranger/pdfarranger/releases/download/1.10.0/pdfarranger-1.10.0-windows-installer.msi
  InstallerSha256: B77A5DC7C956F1E0986664B0587B9B7532CA304590F4F1C86B03960486DDE4F6
  InstallerSwitches:
    Custom: ALLUSERS=1

However I believe the built-in convenience of winget to automatically know the right parameters for many setup types, including per-user MSI, should be expanded to automatically support per-machine MSI as well so this workaround is no longer needed.

Start by tracing the winget-cli MSI installer handling for manifest entries with Scope: machine and the existing per-user MSI switch behavior. Verify the implementation and tests cover appending ALLUSERS=1 for machine-scope MSI installs, including the --scope machine case, without requiring InstallerSwitches.Custom.