feat(iOS, SplitView): Add an option for changing number of columns dynamically (#3339)

## Description

Previously, the constructor of UISplitViewController relied on a
predefined number of columns, and we enforced this constraint using
an assert to prevent unexpected runtime behavior when the number of
children changed dynamically.

Inspired by the `expo-router` approach, this PR removes the static
assert and introduces a more dynamic pattern: the `SplitViewHost` now
actively monitors the number of child columns. If the number of children
changes, the entire `UISplitViewController` is remounted to reflect the
updated configuration.

Fixes
software-mansion/react-native-screens-labs#499
.

## Changes

- Added counters to monitor the number of columns and inspectors

## Screenshots / GIFs

Here you can add screenshots / GIFs documenting your change.

You can add before / after section if you're changing some behavior.

### Before


https://github.com/user-attachments/assets/8474db46-9c87-4523-a6fc-effae0ad8555


### After


https://github.com/user-attachments/assets/7a5522c2-c9c8-4afe-8b1f-a3144f97b140


## Test code and steps to reproduce

Run any example with SplitView and add/remove columns or inspector.

## Checklist

- [x] Included code example that can be used to test this change
- [x] Ensured that CI passes

Author: t0maboro

src/components/gamma/split-view/SplitViewHost.tsx

@@ -6,6 +6,7 @@ import type {
   SplitViewHostProps,
   SplitViewSplitBehavior,
 } from './SplitViewHost.types';
+import SplitViewScreen from './SplitViewScreen';
 
 // According to the UIKit documentation: https://developer.apple.com/documentation/uikit/uisplitviewcontroller/displaymode-swift.enum
 // Only specific pairs for displayMode - splitBehavior are valid and others may lead to unexpected results.
@@ -59,8 +60,26 @@ function SplitViewHost(props: SplitViewHostProps) {
     }
   }, [preferredDisplayMode, preferredSplitBehavior]);
 
+  const children = React.Children.toArray(props.children);
+
+  const columns = children.filter(
+    // @ts-ignore - type is valid attribute for child
+    child => child.type === SplitViewScreen.Column,
+  );
+
+  const inspectors = children.filter(
+    // @ts-ignore - type is valid attribute for child
+    child => child.type === SplitViewScreen.Inspector,
+  );
+
   return (
-    <SplitViewHostNativeComponent {...props} style={styles.container}>
+    <SplitViewHostNativeComponent
+      // UISplitViewController requires the number of columns to be specified at initialization and it cannot be changed dynamically later.
+      // By using a specific key in this form, we can detect changes in the number of React children.
+      // This enables us to fully recreate the SplitView when necessary, ensuring the correct column configuration is always applied.
+      key={`columns-${columns.length}-inspectors-${inspectors.length}`}
+      {...props}
+      style={styles.container}>
       {props.children}
     </SplitViewHostNativeComponent>
   );