For whatever reason, `ExtractIconEx` returns icons whose sizes are
inappropriate for the current DPI, resulting in terribly-blurry
window icons at higher DPIs.
To solve this, the window icon is now set to the first icon group
that is present in the executable. This behaviour should match what
Explorer does. By selecting an icon group instead of a specific icon,
Windows is free to select the icon within the group that best suits
the current DPI.
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