Converts unity android runtime permission API to async

AndroidRuntimeAsyncPermissionService.cs

using System.Threading.Tasks;
using UnityEngine;
using UnityEngine.Android;

//see https://docs.unity3d.com/ScriptReference/Android.Permission.html
//see https://docs.unity3d.com/6000.0/Documentation/ScriptReference/Android.PermissionCallbacks.html
public static class AndroidRuntimeAsyncPermissionService
{
    public static async Task<PermissionResult> RequestPermissionAsync(string permission)
    {
        // If the user has already granted permission, return Granted
        if (Permission.HasUserAuthorizedPermission(permission))
        {
            return PermissionResult.Granted;
        }

        // Otherwise, request permission
        var tcs = new TaskCompletionSource<PermissionResult>();
        var callbacks = new PermissionCallbacks();

        // Define the callback events
        callbacks.PermissionGranted += OnPermissionGranted;
        callbacks.PermissionDenied += OnPermissionDenied;
        callbacks.PermissionDeniedAndDontAskAgain += OnPermissionDeniedAndDontAskAgain;

        // Request the permission
        Permission.RequestUserPermission(permission, callbacks);

        // Await the completion of the permission request
        return await tcs.Task;

        // Local callback methods
        void OnPermissionGranted(string permissionName)
        {
            if (permissionName == permission)
            {
                tcs.SetResult(PermissionResult.Granted);
                CleanupCallbacks();
            }
        }

        void OnPermissionDenied(string permissionName)
        {
            if (permissionName == permission)
            {
                tcs.SetResult(PermissionResult.Denied);
                CleanupCallbacks();
            }
        }

        void OnPermissionDeniedAndDontAskAgain(string permissionName)
        {
            if (permissionName == permission)
            {
                tcs.SetResult(PermissionResult.DeniedAndDontAskAgain);
                CleanupCallbacks();
            }
        }

        void CleanupCallbacks()
        {
            callbacks.PermissionGranted -= OnPermissionGranted;
            callbacks.PermissionDenied -= OnPermissionDenied;
            callbacks.PermissionDeniedAndDontAskAgain -= OnPermissionDeniedAndDontAskAgain;
        }
    }

    public enum PermissionResult
    {
        Granted,
        Denied,
        DeniedAndDontAskAgain
    }
}

// Example usage:
// var result = await AndroidRuntimeAsyncPermissionService.RequestPermissionAsync("android.permission.POST_NOTIFICATIONS");
// Debug.Log($"Push notification permission result: {result}");