Upgrade to .NET 8 (and re-write some MVMM components)

[aspriddell]

Aside from upgrading to .NET 8, this also redoes some of the core functionality making it work in line with expectations:

• Rewritten the removal logic to use a single model instead of multiple viewmodels
• Split the logic and view contents to adhere to mvvm better
• Disable error reporting on non-deployed builds
• Remove MessageBus usage, use interactions as a replacement
• Fix the package list not getting reloaded on the progress window closing
• Fix removed packages not getting deselected once removed
• Improve removal progress page text truncation/trimming
• Update year in about page
• Update AvaloniaUI
• Remove redundant packages

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