split property
When true, splits items between left and right sections.
This follows Apple's HIG guidelines for organizing related tab functions into logical groups with clear visual separation.
Note: With a searchItem, the iOS 26+ bar is one bar whose last tab is the search tab, and split is ignored; the Flutter fallback below iOS 26 puts the search button on the right.
macOS has no split tab bar; there the tabs stay in one control.
Implementation
final bool split;