[IMPROVEMENT] "Manage ignored updates" Pop-Up Window

[Meteony]

Please confirm these before moving forward.

• I have searched for my feature proposal and have not found a work-in-progress/duplicate/resolved/discarded issue.
• This improvement refers to an existing feature. If you want to suggest a new feature, please use this template.
• This improvement is not a bug. If you want to report a bug, please use this template.

Describe the improvement

Previously "manage ignored updates" opens up an overlay window inside the main app frame, which makes it way more adaptive to different main window sizes.

After the Avalonia rewrite, the dialog has now become a pop-up window that is too wide, doesn't remember its own sizing, and is arguably less visually coherent.

Reverting to the previous design pattern could bring real, tangible benefits to the user experience.

Describe how this improvement could help users

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[Meteony]

Gabriel Dufresne (@GabrielDuf)

I tested the newest commit. A few things I've found so far:

1. The current implementation spawns a secondary window instance. While valid, WinUI generally spawns a false window overlay within the primary window that moves & resizes with the main app with a nice transition animation.
   You can see from the image that "manage ignored update" isn't its own window, but rather an overlay frame drawn within UniGetUI's instance. This might not be as straightforward in Avalonia to implement, but since UniGetUI already manages its own titlebar anyway, it shouldn't be impossible.

There's another reason why I think it should be done:

2. Current UniGetUI's pop-up windows all have their own maximize & minimize controls, which stems from the same issue - they are their own individual windows. However, those are really buggy with weird linked viability states (e.g. minimizing one pop-up causes everything to collapse), and probably weren't really intended to be there at the first place. They should be removed at least.

3. "Package Details" menu has the same problem ([BUG] Inner window cannot be closed - buttons are outside of the display area #5189). Same with other pop-ups, such as cli output, About UniGetUI, Installation Options (Software Updates) (which is also it's missing the Invalid Selection toast, I just found out).

Those should be revised as well.