Add fallback for ForegroundServiceStartNotAllowedException in Android 31+ (#6808)

Task/Issue URL:
https://app.asana.com/1/137249556945/project/1202552961248957/task/1206535923706701?focus=true

### Description
Work around platform bug
([b/229000935](https://issuetracker.google.com/issues/229000935)) where
startForegroundService() for
VpnService can throw ForegroundServiceStartNotAllowedException when
called
from background. We now catch this and fall back to startService(),
which
is allowed for VPNs. Service still promotes itself to foreground as
usual.


### Steps to test this PR
Smoke test AppTP and VPN on off scenarios for Android on 31+ and below
31

Author: aitorvs

app-tracking-protection/vpn-impl/src/main/java/com/duckduckgo/mobile/android/vpn/service/TrackerBlockingVpnService.kt

@@ -18,6 +18,7 @@ package com.duckduckgo.mobile.android.vpn.service
 
 import android.annotation.SuppressLint
 import android.app.ActivityManager
+import android.app.ForegroundServiceStartNotAllowedException
 import android.app.Service
 import android.content.ComponentName
 import android.content.Context
@@ -815,7 +816,7 @@ class TrackerBlockingVpnService : VpnService(), CoroutineScope by MainScope(), V
             if (!isServiceRunning(appContext)) return
 
             snoozeIntent(appContext, triggerAtMillis).run {
-                ContextCompat.startForegroundService(appContext, this)
+                appContext.startForegroundServiceWithFallback(this)
             }
         }
 
@@ -842,7 +843,7 @@ class TrackerBlockingVpnService : VpnService(), CoroutineScope by MainScope(), V
             if (isServiceRunning(applicationContext)) return
 
             startIntent(applicationContext).run {
-                ContextCompat.startForegroundService(applicationContext, this)
+                applicationContext.startForegroundServiceWithFallback(this)
             }
         }
 
@@ -852,15 +853,15 @@ class TrackerBlockingVpnService : VpnService(), CoroutineScope by MainScope(), V
             if (!isServiceRunning(applicationContext)) return
 
             stopIntent(applicationContext).run {
-                ContextCompat.startForegroundService(applicationContext, this)
+                applicationContext.startForegroundServiceWithFallback(this)
             }
         }
 
         private fun restartService(context: Context) {
             val applicationContext = context.applicationContext
 
             restartIntent(applicationContext).run {
-                ContextCompat.startForegroundService(applicationContext, this)
+                applicationContext.startForegroundServiceWithFallback(this)
             }
         }
 
@@ -883,6 +884,23 @@ class TrackerBlockingVpnService : VpnService(), CoroutineScope by MainScope(), V
             }
         }
 
+        @SuppressLint("DenyListedApi") // static private method
+        private fun Context.startForegroundServiceWithFallback(intent: Intent) {
+            try {
+                ContextCompat.startForegroundService(this, intent)
+            } catch (ex: ForegroundServiceStartNotAllowedException) {
+                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
+                    try {
+                        this.startService(intent)
+                    } catch (_: Throwable) {
+                        // no-op
+                    }
+                } else {
+                    throw ex
+                }
+            }
+        }
+
         private const val ACTION_START_VPN = "ACTION_START_VPN"
         private const val ACTION_STOP_VPN = "ACTION_STOP_VPN"
         private const val ACTION_RESTART_VPN = "ACTION_RESTART_VPN"