fix: Prevent GC'on of native callback

[RussKie]

Fixes #4264

Proposed changes

The native callback can be garbage collected even in a simple app, which leads to an app crash with ExecutionEngineException.
The issue can be observed even in an app as simple as:

namespace repro_listview
{
    static class Program
    {
        [STAThread]
        static void Main()
        {
            Application.SetHighDpiMode(HighDpiMode.SystemAware);
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);

            var f = new Form();
            var listView = new ListView();

            f.Controls.Add(listView);

            listView.Items.Add("A");
            listView.Items.Add("Z");
            listView.Items.Add("X");
            listView.ListViewItemSorter = new TestComparer();

            Application.Run(f);
        }

        class TestComparer : Comparer<ListViewItem>
        {
            public override int Compare(ListViewItem x, ListViewItem y)
            {
                GC.Collect();
                Thread.Sleep(10);
                return 0;
            }
        }
    }
}

Customer Impact

• Interacting with a ListView with sort enabled won't be crashing an app due to a GC'ed native callback.

Regression?

• Yes

Risk

• Minimal

Test methodology

• manual, by replacing binaries in C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App\6.0.0-alpha.1.20570.2
• no automation test could be devised as the problem couldn't be reproduced from the Windows Forms codebase, either 5.0 or 6.0 branches

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Merging #4280 (4b0e22e) into master (12b8059) will increase coverage by 0.00773%.
The diff coverage is n/a.

@@                 Coverage Diff                 @@
##              master       #4280         +/-   ##
===================================================
+ Coverage   97.96185%   97.96958%   +0.00772%     
===================================================
  Files            499         499                 
  Lines         259010      259010                 
  Branches        4569        4569                 
===================================================
+ Hits          253731      253751         +20     
+ Misses          4473        4457         -16     
+ Partials         806         802          -4     

Flag	Coverage Δ
Debug	97.96958% <ø> (+0.00772%)	⬆️
production	100.00000% <ø> (ø)
test	97.96958% <ø> (+0.00772%)	⬆️

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[RussKie]

Thank you @kpreisser for your help repro'ing the issue.