the context can now override a virtual method named `CreateHelpContent` which the setup wizard system will automatically try to use when you use the generic overload taking a generic context type. If the return is null, it skips setting entirely (the default impl is null)
additionally made the discord join link a button with code copied from the about window, and made it centered at the bottom.
- Remove polymorphic base, this only existed because TKMM has a desktop/switch setup prodecure difference and has 2 implementations of the setup wizard. We only need one.
- Remove Systems/UI file split, they're all in Ryujinx.Ava.UI now
- made NotificationHelper instance-based to allow you to encapsulate notifications to a window that magically disappear when the window is closed, instead of switching to showing on the main window.
