iOS textTransform style support

Summary:
Issue [#2088](facebook/react-native#2088).

The basic desire is to have a declarative mechanism to transform text content to uppercase or lowercase or titlecase ("capitalized").

My test plan involves having added a test-case to the RNTester app within the `<Text>` component area.   I then manually verified that the rendered content met my expectation.

Here is the markup that exercises my enhancement:

```
<View>
  <Text style={{ textTransform: 'uppercase'}}>
    This text should be uppercased.
  </Text>
  <Text style={{ textTransform: 'lowercase'}}>
    This TEXT SHOULD be lowercased.
  </Text>
  <Text style={{ textTransform: 'capitalize'}}>
    This text should be CAPITALIZED.
  </Text>
  <Text style={{ textTransform: 'capitalize'}}>
    Mixed:{' '}
    <Text style={{ textTransform: 'uppercase'}}>
      uppercase{' '}
    </Text>
    <Text style={{ textTransform: 'lowercase'}}>
      LoWeRcAsE{' '}
    </Text>
    <Text style={{ textTransform: 'capitalize'}}>
      capitalize each word
    </Text>
  </Text>
</View>
```

And here is a screenshot of the result:

![screen shot 2018-03-14 at 3 01 02 pm](https://user-images.githubusercontent.com/575821/37433772-7abe7fa0-279a-11e8-9ec9-fb3aa1952dad.png)

[Website Documentation PR](facebook/react-native-website#254)
facebook/react-native-website#254

[IOS] [ENHANCEMENT] [Text] - added textTransform style property enabling declarative casing transformations
Closes facebook/react-native#18387

Differential Revision: D7583315

Pulled By: shergin

fbshipit-source-id: a5d22aea2aa4f494b7b25a055abe64799ccbaa79

js/TextExample.ios.js

@@ -860,6 +860,42 @@ exports.examples = [
     title: 'Text `alignItems: \'baseline\'` style',
     render: function() {
       return <TextBaseLineLayoutExample />;
+    }
+  },
+  {
+    title: 'Transform',
+    render: function() {
+      return (
+        <View>
+          <Text style={{ textTransform: 'uppercase'}}>
+            This text should be uppercased.
+          </Text>
+          <Text style={{ textTransform: 'lowercase'}}>
+            This TEXT SHOULD be lowercased.
+          </Text>
+          <Text style={{ textTransform: 'capitalize'}}>
+            This text should be CAPITALIZED.
+          </Text>
+          <Text style={{ textTransform: 'capitalize'}}>
+            Mixed:{' '}
+            <Text style={{ textTransform: 'uppercase'}}>
+              uppercase{' '}
+            </Text>
+            <Text style={{ textTransform: 'lowercase'}}>
+              LoWeRcAsE{' '}
+            </Text>
+            <Text style={{ textTransform: 'capitalize'}}>
+              capitalize each word
+            </Text>
+          </Text>
+          <Text>Should be "ABC":
+            <Text style={{ textTransform: 'uppercase' }}>a<Text>b</Text>c</Text>
+          </Text>
+          <Text>Should be "AbC":
+            <Text style={{ textTransform: 'uppercase' }}>a<Text style={{ textTransform: 'none' }}>b</Text>c</Text>
+          </Text>
+        </View>
+      );
     },
   },
 ];