Opening a context flyout on a text box leaks memory

[BAndysc]

Describe the bug

Opening a context flyout on a text box leaks memory

To Reproduce

1. git clone https://github.com/BAndysc/avalonia-bugs-repro
2. git checkout bug_windows_input_panel
3. Run the app, press the button to open a new window
4. Open a context menu in the text box
5. Close the second window
6. Memory leak:

Expected behavior

No response

Avalonia version

11.0.10, 11.2.999-cibuild0047556-alpha

OS

Windows

Additional context

Target is set here: https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.Controls/Flyouts/PopupFlyoutBase.cs#L238 and will only be released when the next menu is opened

[BAndysc]

@maxkatz6 Target no longer keeps a strong reference, but unfortunately the issue is still valid.

[BAndysc]

The left path is caused by PlacementTarget this time:

[BAndysc]

Actually, it looks like solving this issue is as simple as resetting the value #15478

[BAndysc]

The PR fixes the left path, but there are still other retention paths

[BAndysc]

^ The leak is still valid in the latest nightly, can we reopen this issue or should I open a new issue?