Grant MANAGE_USB permission, so we can get USB serial numbers

This is needed to reliably identify USB mass storage devices.
If someone has several identical thumb drives,
this prevents a backup from being performed when non-backup drives get attached.

app/src/main/AndroidManifest.xml

@@ -14,6 +14,11 @@
         android:name="android.permission.MANAGE_DOCUMENTS"
         tools:ignore="ProtectedPermissions" />
 
+    <!-- This is needed to access the serial number of USB mass storage devices -->
+    <uses-permission
+        android:name="android.permission.MANAGE_USB"
+        tools:ignore="ProtectedPermissions" />
+
     <application
         android:name=".Backup"
         android:allowBackup="false"

app/src/main/java/com/stevesoltys/backup/UsbIntentReceiver.kt

@@ -77,7 +77,7 @@ private fun UsbInterface.isMassStorage(): Boolean {
 
 private fun UsbDevice.log() {
     Log.d(TAG, "  name: $manufacturerName $productName")
-//    Log.d(TAG, "  serialNumber: $serialNumber")  // requires a permission since API 29
+    Log.d(TAG, "  serialNumber: $serialNumber")
     Log.d(TAG, "  productId: $productId")
     Log.d(TAG, "  vendorId: $vendorId")
     Log.d(TAG, "  isMassStorage: ${isMassStorage()}")

app/src/main/java/com/stevesoltys/backup/settings/SettingsManager.kt

@@ -131,7 +131,7 @@ data class FlashDrive(
     companion object {
         fun from(device: UsbDevice) = FlashDrive(
                 name = "${device.manufacturerName} ${device.productName}",
-                serialNumber = "", // device.serialNumber requires a permission since API 29
+                serialNumber = device.serialNumber,
                 vendorId = device.vendorId,
                 productId = device.productId
         )

permissions_com.stevesoltys.backup.xml

@@ -2,5 +2,6 @@
 <permissions>
     <privapp-permissions package="com.stevesoltys.backup">
         <permission name="android.permission.BACKUP"/>
+        <permission name="android.permission.MANAGE_USB"/>
     </privapp-permissions>
 </permissions>