ui: Use curly quotes in UI strings

[chrisbobbe]

If we think it's more polished, we should consistently use curly quotes instead of straight quotes in UI strings. We use curly quotes in zulip-mobile, and in fact tools/test intl helps us enforce that.

So for example, use this:

Please tap “{troubleshootingPageTitle}” for more details.

not this:

Please tap "{troubleshootingPageTitle}" for more details.

And use this:

What’s your status?

not this:

What's your status?