Fix nested buttons on the new architecture (#2926)

## Description

On the new architecture, due to composing `RNGestureHandlerButton` and
`RNGestureHandlerButtonComponentView` the native view hierarchy wasn't
representative of the hierarchy in the React Native. The most outer
button would be rendered on top of all the react children, swallowing
all the touches and preventing nested buttons from working.

This PR changes the behavior by mounting all children under the actual
button view, which should result in the correct native hierarchy.

## Test plan

<details>
<summary>Tested on the example app and on the following code:</summary>

```jsx
import { SafeAreaView, View } from 'react-native';
import {
  GestureHandlerRootView,
  TouchableOpacity,
} from 'react-native-gesture-handler';

export default function App() {
  return (
    <GestureHandlerRootView style={{ flex: 1 }}>
      <SafeAreaView style={{ flex: 1 }}>
        <TouchableOpacity
          onPress={() => {
            console.log('outer press');
          }}>
          <View style={{ width: 200, height: 200, backgroundColor: 'red' }}>
            <TouchableOpacity
              onPress={() => {
                console.log('inner press');
              }}>
              <View
                style={{
                  width: 100,
                  height: 100,
                  backgroundColor: 'blue',
                }}
              />
            </TouchableOpacity>
          </View>
        </TouchableOpacity>
      </SafeAreaView>
    </GestureHandlerRootView>
  );
}
```
</details>

apple/RNGestureHandlerButtonComponentView.mm

@@ -34,6 +34,16 @@ - (instancetype)initWithFrame:(CGRect)frame
   return self;
 }
 
+- (void)mountChildComponentView:(UIView<RCTComponentViewProtocol> *)childComponentView index:(NSInteger)index
+{
+  [_buttonView mountChildComponentView:childComponentView index:index];
+}
+
+- (void)unmountChildComponentView:(UIView<RCTComponentViewProtocol> *)childComponentView index:(NSInteger)index
+{
+  [_buttonView unmountChildComponentView:childComponentView index:index];
+}
+
 #pragma mark - RCTComponentViewProtocol
 
 + (ComponentDescriptorProvider)componentDescriptorProvider