Add TextTransform KTX (#47525)

Summary:
Pull Request resolved: #47525

This API is awkward for nullsafe code.  Adding an extension allows Kotlin code to use `applyTextTransform()` on either nullable or non-null strings:
```
val a: String = string.applyTextTransform(...)
val b: String? = nullableString?.applyTextTransform(...)
```
Changelog:
[Android][Added] TextTransform ktx

Reviewed By: javache

Differential Revision: D65618709

fbshipit-source-id: 28a0fe61a0eaf27aa9677af39d932982f3b694b2

packages/react-native/ReactAndroid/api/ReactAndroid.api

@@ -7598,6 +7598,10 @@ public final class com/facebook/react/views/text/TextTransform$Companion {
 	public final fun apply (Ljava/lang/String;Lcom/facebook/react/views/text/TextTransform;)Ljava/lang/String;
 }
 
+public final class com/facebook/react/views/text/TextTransformKt {
+	public static final fun applyTextTransform (Ljava/lang/String;Lcom/facebook/react/views/text/TextTransform;)Ljava/lang/String;
+}
+
 public class com/facebook/react/views/text/frescosupport/FrescoBasedReactTextInlineImageViewManager : com/facebook/react/uimanager/BaseViewManager {
 	public static final field REACT_CLASS Ljava/lang/String;
 	public fun <init> ()V

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/text/TextTransform.kt

@@ -21,35 +21,28 @@ public enum class TextTransform {
 
   public companion object {
     @JvmStatic
-    public fun apply(text: String?, textTransform: TextTransform?): String? {
-      if (text == null) {
-        return null
-      }
-      val transformed: String =
-          when (textTransform) {
-            UPPERCASE -> text.uppercase(Locale.getDefault())
-            LOWERCASE -> text.lowercase(Locale.getDefault())
-            CAPITALIZE -> capitalize(text)
-            else -> text
-          }
-      return transformed
-    }
+    public fun apply(text: String?, textTransform: TextTransform?): String? =
+        text?.applyTextTransform(textTransform)
+  }
+}
 
-    private fun capitalize(text: String): String {
+public fun String.applyTextTransform(textTransform: TextTransform?): String {
+  return when (textTransform) {
+    TextTransform.UPPERCASE -> uppercase(Locale.getDefault())
+    TextTransform.LOWERCASE -> lowercase(Locale.getDefault())
+    TextTransform.CAPITALIZE -> {
       val wordIterator = BreakIterator.getWordInstance()
-      wordIterator.setText(text)
-
-      val res = StringBuilder(text.length)
+      wordIterator.setText(this)
+      val res = StringBuilder(length)
       var start = wordIterator.first()
       var end = wordIterator.next()
       while (end != BreakIterator.DONE) {
-        res.append(text[start].uppercaseChar())
-        res.append(text.substring(start + 1, end))
+        res.append(substring(start, end).replaceFirstChar { it.uppercaseChar() })
         start = end
         end = wordIterator.next()
       }
-
-      return res.toString()
+      res.toString()
     }
+    else -> this
   }
 }