R1:020df6f5cb80

Add a numeric input control for TOTP codes

Summary:
Fixes T11365. I tested these variants:

- `<input type="number" />`
- `<input type="text" pattern="\d*" />`

Of these, this one (using `pattern`) appears to have the best behavior: it shows the correct keyboard on iOS mobile and does nothing on desktops.

Using `type="number"` causes unwanted sub-controls to appear in desktop Safari, and a numbers + symbols keyboard to appear on iOS (presumably so users can type "." and "-" and maybe ",").

Test Plan…