Throughout the application lifecycle, we may close or open these windows for various reasons (display changes, preference changes, etc). Unfortunately, previously these windows would always remain in memory after being closed, for multiple reasons. The changes in this PR plug the leaks that were causing this to happen.

Menu bar

• Fixed event handler and timer leaks in Clock and Search menu bar extras
• Fixed AppBarWindow leak via ManagedShell update

Desktop

• Fixed NavigationManager never being disposed
• Fixed event handler leak in DesktopIcons and NavigationManager

Taskbar

• Multiple fixes for AppGrabberTaskCategoryProvider
  • Fixed the taskbar creating multiple instances of the provider, when only one is needed at a time, by moving the logic to TaskbarWindowService
  • Fixed event handler leaks in the class
  • Fixed CategoryChanged event for the "All" category causing unnecessary work
  • Also fixed TryGetCategoryDisplayNameByProcId to not return the current window
• Fixed event handler leak in QuickLaunchButton and Taskbar
• Fixed task button animations to no longer keep references to the control
• Fixed AppBarWindow leak via ManagedShell update