Support returning currently displayed text onTap

**Describe the solution you'd like**
```dart
AnimatedTextKit(
onTap: (String currentText) {
// I can do something with currentText here.
}
)
```

**Additional context**
This is useful for animated text kit in the search bar, which users can quickly tap to the displayed text to search for it.

Look at the AnimatedTextKit widget's source code, likely in lib/animated_text_kit.dart. Identify where the onTap callback is handled and where the currently displayed text is stored. Modify the onTap signature to pass the current text string. Update any internal logic and ensure all animation types (like TypewriterAnimatedText, FadeAnimatedText) provide the text. Test by running the example app and verifying the callback receives the correct text.

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