[Bug] DataGrid styles inconsistencies

[sn4k3]

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Description of the issue

Found some inconsistencies in styles of DataGrid

1. Lack of styles for groups (DataGridCollectionView)
2. Size of cells are incorrect (Overflowing) causing bad alignment and text out of cell limit
3. GridLinesVisibility="All" also lacks of styles, making borders white instead of copy the border of the header

Package Version

6.0.0-beta6

Environment

Windows 11

Expected Behavior

1. Group expander to have matching style
2. Cells to have proper bounds
3. GridLinesVisibility="All" to have matching style

Reproduction

public partial class TestUserControl : UserControl
{
    public class TestClass
    {
        public int Index { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }
        public string Group { get; set; }
    }

    public ObservableCollection<TestClass> TestCollection { get; } =
    [
        new() { Index = 1, Name = "Test 1", Description = "Description 1", Group = "Group 1"},
        new() { Index = 2, Name = "Test 2", Description = "Description 2", Group = "Group 1" },
        new() { Index = 3, Name = "Test 3", Description = "Description 3", Group = "Group 2" },
        new() { Index = 4, Name = "Test 4", Description = "Description 4", Group = "Group 2" },
    ];


    public TestUserControl()
    {
        InitializeComponent();
        DataContext = this;
    }

    protected override void OnLoaded(RoutedEventArgs e)
    {
        base.OnLoaded(e);
        var groupView = new DataGridCollectionView(TestCollection);
        groupView.GroupDescriptions.Add(new DataGridPathGroupDescription("Group"));
        MyGrid.ItemsSource = groupView;
    }
}

<UserControl xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:views="clr-namespace:NetSonar.Avalonia.Views"
             xmlns:suki="https://github.com/kikipoulet/SukiUI"
             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
             x:Class="NetSonar.Avalonia.Views.TestUserControl"
             x:DataType="views:TestUserControl">
    <UserControl.Styles>
        <Style Selector="DataGridCell.center">
            <Setter Property="HorizontalContentAlignment" Value="Center" />
        </Style>
    </UserControl.Styles>

    <suki:GlassCard>
        <DataGrid Name="MyGrid" GridLinesVisibility="All" ItemsSource="{Binding TestCollection}">
          <DataGrid.Columns>
              <DataGridTextColumn Header="Index" Binding="{Binding Index}" CellStyleClasses="center"/>
              <DataGridTextColumn Header="Name" Binding="{Binding Name}"/>
              <DataGridTextColumn Header="Description" Binding="{Binding Description}"/>
              <DataGridTextColumn Header="Group" Binding="{Binding Group}"/>
          </DataGrid.Columns>
      </DataGrid>
    </suki:GlassCard>
</UserControl>

Additional Information

No response