feat: Create CustomList

[RemiBardon]

Following a Slack discussion on #78 (comment), we decided to reimplement a basic SwiftUI List using a VStack.

I managed to recreate a good portion of the List API, or at least what we will need of it.

Here are the results:

When the window is not key:

With sections (supports .headerProminence(.increased)):

I had to create a custom selection shape, to get the same effect as List when multiple items are selected and touch each other:

There is no support for keyboard navigation. This must be implemented higher in the hierarchy, or I can implement it here as well if needed. The higher implementation will be necessary anyway, when the list is not first responder, which is the only place where we will use CustomList, so I don't think we need to duplicate this code.

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Initial TODO list from #78:

• Accept a view for its cells provided from outside
• Bind its selection to the ViewStore
• Handle loading, error and empty states
• Its state offers convenience methods to manipulate the list selection

[RemiBardon]

I'll just add an initializer which takes sectionned content but a single selection, I need it for #78.

[RemiBardon]

I just tested with the attached window, and it works (using .fixedSize(horizontal: true, vertical: false) for rows and header. I did not enforce this in my CustomList implementation, should I? It would prevent us from creating rows with content on both sides… which is very unfortunate. I couldn't find a workaround… yet.

Also, the attached window is not key, so it gives this bad result. However, this must be fixed in the other PR, and https://github.com/smic/SuggestionsDemo seems to handle it well. We'll see.

[RemiBardon]

https://github.com/smic/SuggestionsDemo seems to handle it well.

No it does not. I changed a few things to use controlActiveState, and it has the same problem. The text field is first responder, I don't think we can solve this issue.

I will have to add some environment value or value in the initializer to force the usage of .fill(.tint), as the attached window will disappear when the main window is not key anyway.

[RemiBardon]

The magic of SwiftUI: I just added .environment(\.controlActiveState, .active) to the attached window, and it works 🥳

@nesium Should I add this modifier on AttachedWindow itself or are there cases where we won't want to enforce this?