added "REQUEST_INSTALL_PACKAGES" permission

Author: Jan-Derk

permission_handler_platform_interface/lib/src/permissions.dart

@@ -137,7 +137,6 @@ class Permission {
   ///iOS: Nothing
   static const requestInstallPackages = Permission._(24);
 
-
   /// Returns a list of all possible [PermissionGroup] values.
   static const List<Permission> values = <Permission>[
     calendar,

permission_handler_platform_interface/test/src/permissions_test.dart

@@ -6,7 +6,7 @@ void main() {
       () {
     final values = Permission.values;
 
-    expect(values.length, 24);
+    expect(values.length, 25);
   });
 
   test('check if byValue returns corresponding PermissionGroup value', () {