fix: measure custom tab bar height with onLayout

[mrpmohiburrahman]

PR Description

Bug fix. Closes #380.

TabView measured the custom tab bar by calling .measure() on the wrapper View in a useLayoutEffect. Absolutely positioned children don't contribute to their parent's measured size, so for a renderCustomTabBar that returns an absolutely positioned element the wrapper measured 0 and useBottomTabBarHeight() returned 0.

Changes:

• Removed the ref + useLayoutEffect + .measure() logic.
• The element returned by renderCustomTabBar is now cloned with an injected onLayout (any onLayout the element already declares is still called), and the wrapper keeps its own onLayout.
• The reported height is the larger of the two, so regular tab bars keep the wrapper measurement and absolutely positioned ones get the element's own height. Non-element return values (fragments, arrays) still fall back to the wrapper, preserving the previous behaviour.

How to test?

Render a TabView with a custom tab bar that is absolutely positioned, and read the height from a screen:

<TabView
  renderCustomTabBar={() => (
    <View style={{ position: 'absolute', bottom: 0, width: '100%', height: 60, backgroundColor: 'white' }} />
  )}
  // ...
/>

const height = useBottomTabBarHeight(); // 0 before, 60 after

A non-absolutely-positioned custom tab bar should keep reporting the same height as before.

Screenshots

N/A — no visual change to the library itself; the fix affects the value reported by useBottomTabBarHeight().