Add desktop shortcut for applications

Description of the new feature / enhancement

It will be useful for software that does not create desktop shortcuts itself:
steascree
ppsspp
msiafterburner (msi afterburner also contains RTSS software and installer does not create desktop shortcut for it)
handbrake
keepassxc
parsec
dupeguru

And for portable programs like:
pcsx2-dev
yuzu
ryujinx
insomnia
syncthingtray
ds4windows
melonDS.melonDS
Reshade

Similar issue but for start menu shortcuts https://github.com/microsoft/winget-cli/issues/2299

Proposed technical implementation details

Example for AwthWathje.SteaScree non-portable package:

Installers:
- Architecture: x86
  InstallerUrl: https://steascree.download/steascree-1.5.4-windows.exe
  InstallerSha256: DDEB40DE6538F47A6666A656C867261D3349CA01D8F5DD1145B8E74574F270D4
  DesktopShortcut: "${env:ProgramFiles(x86)}\SteaScree\SteaScree.exe" SteaScree

Example for syncthingtray portable package:

Installers:
Installers:
- Architecture: x64
  NestedInstallerType: portable
  NestedInstallerFiles:
  - RelativeFilePath: syncthingtray-1.4.11-x86_64-w64-mingw32.exe
    PortableCommandAlias: syncthingtray
  InstallerUrl: https://github.com/Martchus/syncthingtray/releases/download/v1.4.11/syncthingtray-1.4.11-x86_64-w64-mingw32.exe.zip
  InstallerSha256: 84BB58505DF4E9DE5653352A8357359E8B46D8376E0D6E7E197B0C6786F1C8FB
  DesktopShortcut: <INSTALLPATH>\syncthingtray-1.4.11-x86_64-w64-mingw32.exe SyncthingTray

Start by reviewing the winget-cli package installation and shortcut-related entry points, then compare the proposed DesktopShortcut examples for non-portable and portable packages. Use the linked start-menu shortcut issue as related context. Done means supported package definitions can create desktop shortcuts for both installer types without breaking existing installation behavior.