fix: new arch invalidate on mount/unmount (#2318)

# Summary

On iOS with the new architecture, when mounting or unmounting a
component, changes were not visible because `invalidate` wasn't called.
These changes override `mountChildComponentView` and
`unmountChildComponentView` to ensure that invalidate is called when
`RNSVGNode` is mounted or unmounted.

## Test Plan

`TestExample` app -> `MountUnmount` example 

```tsx
import React from 'react';
import {Button, Text, View} from 'react-native';
import {Rect, Svg} from 'react-native-svg';

export default () => {
  const [show, setShow] = React.useState(true);
  return (
    <View style={{flex: 1, justifyContent: 'center', alignItems: 'center'}}>
      <Text>Blue rect is mounted: {show ? 'true' : 'false'}</Text>

      <Svg height="300" width="300">
        {show ? (
          <Rect x="100" y="100" width="100" height="100" fill="blue" />
        ) : null}
      </Svg>
      <Button title="Toggle" onPress={() => setShow(!show)} />
    </View>
  );
};
```


https://github.com/software-mansion/react-native-svg/assets/39670088/0eaf9a61-b47b-4f89-a7c7-a67375e2e63e


https://github.com/software-mansion/react-native-svg/assets/39670088/709feedf-63c1-47d7-b799-f3899278fe77


## Compatibility

| OS      | Implemented |
| ------- | :---------: |
| iOS     |    ✅     |

apple/RNSVGNode.mm

@@ -59,6 +59,20 @@ CGFloat const RNSVG_DEFAULT_FONT_SIZE = 12;
   [self invalidate];
 }
 
+#ifdef RCT_NEW_ARCH_ENABLED
+- (void)mountChildComponentView:(UIView<RCTComponentViewProtocol> *)childComponentView index:(NSInteger)index
+{
+  [super mountChildComponentView:childComponentView index:index];
+  [self invalidate];
+}
+
+- (void)unmountChildComponentView:(UIView<RCTComponentViewProtocol> *)childComponentView index:(NSInteger)index
+{
+  [super unmountChildComponentView:childComponentView index:index];
+  [self invalidate];
+}
+#endif
+
 - (void)didUpdateReactSubviews
 {
   // Do nothing, as subviews are inserted by insertReactSubview: