Add toast notification infrastructure

[carlos-zamora]

Summary of the Pull Request

Adds the infrastructure for toast notifications. Breakdown:

• DesktopNotification:
  • DesktopNotificationArgs includes the struct to group all notification-related data together.
  • SendNotification() actually sends it
• AppCommandlineArgs.cpp: added a check for the __fromToast no-op sentinel
• Most of the other changes are just bubbling up the notification from the TerminalPaneContent to TerminalPage
• TabManagement.cpp: _SendDesktopNotification() does the final packaging of the notification before calling the DesktopNotification API

This simply adds the infrastructure! Looks like nothing can actually take advantage of it yet

Heavily based on #19935
Co-authored by @zadjii-msft

[carlos-zamora]

Some minor changes from the PR this was based on:

1. Rate-limit race condition: compare_exchange_strong return value is now used directly
2. UI thread safety: SummonWindowRequested is now marshaled to UI thread via Dispatcher().RunAsync()
3. moved some comments around
4. use C++20 designated initializer (and add const)
5. use ApplicationDisplayName() instead of RS_(NotificationTitle) for notification title