FolderPicker: Missing PickMultipleFoldersAsync method

[tipa]

Describe the bug

Similar to the FileOpenPicker to select multiple files, there should be an option for the FolderPicker to allow multiple folders.
A possible use-case where this can be helpful is a photo management software in which the user can select the folders which he wants to add. Adding folders one-by-one can be tedious.
The Win32 APIs should allow this by using the FOS_ALLOWMULTISELECT flag that already is used in the FileOpenPicker:

WindowsAppSDK/dev/Interop/StoragePickers/FileOpenPicker.cpp

Line 149 in f3a179c

check_hresult(dialog->SetOptions(dialogOptions | FOS_ALLOWMULTISELECT));

Steps to reproduce the bug

var savePicker = new FolderPicker(appWindowId);
var result = await savePicker.PickMultipleFoldersAsync(); // does not exist

Expected behavior

No response

Screenshots

No response

NuGet package version

Windows App SDK 1.8.0: 1.8.250907003

Packaging type

Packaged (MSIX)

Windows version

Windows 11 version 24H2 LTSC (26100, June Update)

IDE

Visual Studio 2022

Additional context

No response