Display the wsl node in FolderPicker and FileSavePicker dialog navigation

[DinahK-2SO]

Problem

The WSL navigation node (\\wsl.localhost) is hidden in the navigation pane of FolderPicker and FileSavePicker dialogs due to undocumented behavior in the Windows Common Item Dialog. FileOpenPicker is unaffected.

Fix

PickerCommon::WslNodeRevealer - a per-dialog IFileDialogEvents handler - is registered before Show(). On the first OnFolderChange it:

1. Walks IServiceProvider -> SID_STopLevelBrowser -> IShellBrowser -> INameSpaceTreeControl.
2. Resolves the WSL root shell item (\\wsl.localhost, falling back to \\wsl$).
3. Polls (10 ms, up to 1 s) for navigation-pane root nodes to load; when the WSL node is found among their children, calls INameSpaceTreeControl::SetItemState to reveal it.

Changes

• PickerCommon.h / PickerCommon.cpp — Added WslNodeRevealer with per-instance state. PollTimerProc is static (required by TIMERPROC); all other methods are non-static.
• FileSavePicker.cpp — Register WslNodeRevealer in PickSaveFileAsync.
• FolderPicker.cpp — Register WslNodeRevealer in PickSingleFolderAsync and PickMultipleFoldersAsync.

After Fix

• FolderPicker:
  
• FileSavePicker:
  

Before Fix

• FolderPicker:
  
• FileSavePicker:
  

[DinahK-2SO]

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[DinahK-2SO]

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[DinahK-2SO]

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