Add a setting for sending a notification on BEL

[carlos-zamora]

Summary of the Pull Request

Targets #20010

Adds another bellStyle flag option. This sends a windows toast notification to the user when a BEL is encountered

• Closes Windows Notification on Bell #18605
• Documentation updated

Heavily based on #19936
Co-authored by @zadjii-msft

[carlos-zamora]

The only change I made was I changed the settings UI string from "Send notification" to "Desktop notification"

Separately, I noticed that the default here is audible. A few related questions:

1. Any interest in adding "desktop notification" as the default too?
   • I'm leaning "no". Particularly because I know that I hit a BEL in WSL every time I backspace into the prompt and that would be annoying haha. Wanted to poll for opinions though.
2. visual in the JSON maps to window + taskbar. Should notification be added here too?
   • Kinda torn. It is visual, but it's also kinda outside the frame of the terminal, so I feel like it's a completely different thing.

I also played around with it and I noticed this:

1. open WSL - Ubuntu terminal
2. create BEL (backspace into prompt)
3. Get notification

4. Click notification 5. Get a new Terminal window!

I double checked and we are hitting this code in AppCommandlineArgs::ParseArgs() as expected:

terminal/src/cascadia/TerminalApp/AppCommandlineArgs.cpp

Lines 1071 to 1078 in 4357c17

	// When a toast notification is clicked, Windows may launch a new instance
	// with "__fromToast" as the argument. This is a no-op sentinel — the
	// in-process Activated handler on the toast already handled activation.
	// See DesktopNotification.cpp for more details.
	if (args.size() == 2 && args[1] == L"__fromToast")
	{
	return 0;
	}

Shouldn't we refocus the tab/pane that sent the notification instead? @zadjii-msft thoughts?