macos: hide application from dock

## Feature Request

There is no obvious way to hide an application from the dock on macOS. A number of conventional things like modifying the Info.plist file to include `LSUIElement` don't work. The only way I've found, after hours of fiddling, is to use `dioxus::desktop::tao` directly, then do something like this:

```rust
use dioxus::desktop::tao::platform::macos::{ActivationPolicy, EventLoopWindowTargetExtMacOS};

let dioxus_config = DioxusConfig::new()
.with_custom_event_handler(|_event, event_loop_target| {
// Set activation policy to Accessory on macOS to prevent dock icon
#[cfg(target_os = "macos")]
{
static POLICY_SET: std::sync::Once = std::sync::Once::new();
POLICY_SET.call_once(|| {
event_loop_target
.set_activation_policy_at_runtime(ActivationPolicy::Accessory);
});
}
});
```

I'm only just exploring Dioxus, so it's possible that I'm missing something.

## Implement Suggestion

There should be a single, documented, supported way to hide apps from the dock. I'm agnostic about the exact phrasing of this, as long as it exists.