Update opacity when disabled prop is changed

Summary:
fixes #17105

If you render

```
    <TouchableOpacity
        disabled={true}
        style={{opacity: 0.5}}
    >
        ...
    </TouchableOpacity>
```

and then

```
    <TouchableOpacity
        disabled={false}
        style={{opacity: 1}}
    >
        ...
    </TouchableOpacity>
```

The content of `TouchableOpacity` will still have opacity = 0.5 because real
opacity is controlled by animated property which should be properly updated
when `disabled` prop changes.

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Usually when a button or other UI component is built with `TouchableOpacity` you may want to change it's opacity if state of component is changed (enabled/disabled). Opacity provided in props is overridden with internally-managed animated value. Add extra check when component is updated to trigger opacity animation upon change of `disabled` flag.

You can use code from https://github.com/facebook/react-native/issues/17105.

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/facebook/react-native-website, and link to your PR here.)

[GENERAL][BUGFIX][TouchableOpacity] - trigger animation on `opacity` upon change in `disabled` prop.
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[ INTERNAL ]   [ ENHANCEMENT ]   [ {File}      ]
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 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
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Closes https://github.com/facebook/react-native/pull/17106

Differential Revision: D7158549

Pulled By: hramos

fbshipit-source-id: 209cc433b829b129810e8a884964c8853ca3fe8f

Libraries/Components/Touchable/TouchableOpacity.js

@@ -160,6 +160,12 @@ const TouchableOpacity = createReactClass({
     ensurePositiveDelayProps(nextProps);
   },
 
+  componentDidUpdate: function(prevProps, prevState) {
+    if (this.props.disabled !== prevProps.disabled) {
+      this._opacityInactive(250);
+    }
+  },
+
   /**
    * Animate the touchable to a new opacity.
    */