Provide option to control whether UI is RTL or LTR

Steps to reproduce:

• open Inkscape.AppImage
• change the language to Arabic
• restart Inkscape

What happened?

The interface remains as LTR

What should have happened?

The interface should be RTL

Inkscape Version and Operating System:

• Inkscape Version: Inkscape 1.1-beta1 (inkscape@77e7b44d, 2021-03-28)
• Operating System: Linux Debian 10.9
• Operating System version: Debian GNU/Linux 10 (buster)