Fix keyboard number type

[petrbela]

Numeric/decimal keyboardType should also set type=number to allow only numeric keys on desktop and mobile.

[petrbela]

Related to numeric input, could RNW also support min, max and step? I know they don't exist in RN but they'd simply be ignore there. I can add it to this PR or create a separate one.

[necolas]

See #1709

[petrbela]

@necolas Fair enough. Would you be instead okay with adding web-only type, min, max, and step props to enable explicitly enforcing specific browser behavior when the developer chooses to do so?

[necolas]

I don't think so, as that would puncture the API and allow completely different results to be produced on web.

You can either implement that functionality cross platform in JS, or use the unstable_createElement API to create a custom web element using those props, and decide where to fork/recombine that with your RN code in your product.

[necolas]

But this is a relevant issue for future xplat react APIs, as it surfaces more limitations of RN's TextInput API