fix: avoid clearing active filter text in delayed desktop.ini task

[marko1olo]

Problem

Fixes #18807.

When opening a folder with the filter bar enabled, typing into the filter textbox shortly after navigation starts gets wiped out 1–2 seconds later when the directory load finishes.

Cause

NavigateToPath in ModernShellPage.xaml.cs already resets ShellViewModel.FilesAndFoldersFilter = null; when navigation begins. However, desktopIniUpdateTask was scheduled on DispatcherQueuePriority.Low and also set FilesAndFoldersFilter = null; upon completion, clearing whatever filter query the user had already entered while the folder was loading.

Solution

Remove the redundant and delayed FilesAndFoldersFilter = null; from desktopIniUpdateTask.

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[Josh65-2201]

Duplicate of #18809 also has many unnecessary changes