Dir="auto" for composer and elsewhere

[Osama]

@david

I think we’ll need to keep this. Setting dir="auto" on a textarea will use a heuristic to decide the direction of the entire textarea. That doesn’t sound too useful if you’re writing a post which contains a combination of rtl and ltr languages. So I think the button is required for you to switch back & forth while editing?

Yes, exactly, the button is very useful when you’re typing a post that mixes RTL and LTR languages.

Your PR LGTM @david