Add number-pad keyboardType

Summary:
On Android there's no number-pad but numeric instead, for my use-case I need number only (without decimal and sign, for PIN input)

I write it so there's no breaking change for those already using the `TextInput` Component

None

[ANDROID][ENHANCEMENT][Component] Add number-pad keyboardType
Closes https://github.com/facebook/react-native/pull/18350

Reviewed By: achen1

Differential Revision: D7269721

Pulled By: mdvacca

fbshipit-source-id: 82571dce948e0cf2e4354dc46c69198ec69ba65a

Libraries/Components/TextInput/TextInput.js

@@ -244,6 +244,7 @@ const TextInput = createReactClass({
      *
      * - `default`
      * - `numeric`
+     * - `number-pad`
      * - `email-address`
      * - `phone-pad`
      *
@@ -254,7 +255,6 @@ const TextInput = createReactClass({
      * - `ascii-capable`
      * - `numbers-and-punctuation`
      * - `url`
-     * - `number-pad`
      * - `name-phone-pad`
      * - `decimal-pad`
      * - `twitter`
@@ -272,11 +272,11 @@ const TextInput = createReactClass({
       'email-address',
       'numeric',
       'phone-pad',
+      'number-pad',
       // iOS-only
       'ascii-capable',
       'numbers-and-punctuation',
       'url',
-      'number-pad',
       'name-phone-pad',
       'decimal-pad',
       'twitter',