ipn: provide subtitle in QuickToggleService

[agottardo]

Fixes ENG-3443

As discussed during design review, provides a "Connected" / "Not connected" subtitle in the Tailscale quick tile.

Also drops unnecessary SDK version checks in App.kt.

[oxtoacart]

This may not be new to this PR, but on my Galaxy S23 running Android 14, I see the below problem.

1. Turn on Tailscale
2. Connect to VPN
3. Stop Tailscale (don't disconnect, just stop the app, for example using "Force Quit"). This way, the next time you start Tailscale it'll automatically connect to VPN.
4. Make sure you've enabled our Quick Settings tile
5. Start Tailscale
6. See that Tailscale automatically connects to Tailnet
7. Look at Quick Settings tile and see that styling and text indicate it is disconnected

[agottardo]

This may not be new to this PR, but on my Galaxy S23 running Android 14, I see the below problem.

1. Turn on Tailscale
2. Connect to VPN
3. Stop Tailscale (don't disconnect, just stop the app, for example using "Force Quit"). This way, the next time you start Tailscale it'll automatically connect to VPN.
4. Make sure you've enabled our Quick Settings tile
5. Start Tailscale
6. See that Tailscale automatically connects to Tailnet
7. Look at Quick Settings tile and see that styling and text indicate it is disconnected

I'm opening a separate issue for this; I can also reproduce but I'm unfamiliar with the rest of the tile machinery.