Experiment with RTL layout

[gnprice]

Flutter's API is designed to thoroughly support working in a right-to-left layout direction, as well as left-to-right. It'd be neat to experiment with that; see how much works immediately out of the box; and then see how hard it is to fix up any places where we've introduced an assumption of a left-to-right layout.

This would be a feature that no existing Zulip client supports. If you try switching the Zulip web app to Arabic, for example, basically none of the layout changes — it's all still laid out for LTR.

I think the basic way to test this will look like:

• Where we construct a MaterialApp in lib/widgets/app.dart, add a supportedLocales argument that says we support some RTL locale, like Persian or Arabic or Hebrew. (By default it doesn't assume we support anything but en_US.)
• Then in your device's system settings, set that as your preferred locale.
• See how the app responds.

[gnprice]

@naderm11 has kindly done this experiment, and reports that it works well out of the box. So, closing this issue as complete.

If in the future we find areas where our layout doesn't behave properly in RTL, we can open specific issues for those.