change emoji popup position when too low

modules/expo-emoji-picker/ios/EmojiPickerView.swift

@@ -19,9 +19,19 @@ class EmojiPickerView: ExpoView, MCEmojiPickerDelegate {
     let reactRootVC = reactViewController()
     emojiPicker.sourceView = self
     emojiPicker.delegate = self
+    emojiPicker.arrowDirection = preferredArrowDirection()
     reactRootVC?.present(emojiPicker, animated: true)
   }
 
+  /// If the trigger sits in the bottom third of the screen there isn't enough
+  /// room below it for a usable popover, so anchor the picker above instead.
+  private func preferredArrowDirection() -> MCPickerArrowDirection {
+    guard let window = self.window else { return .up }
+    let frameInWindow = self.convert(self.bounds, to: window)
+    let threshold = window.bounds.height * (2.0 / 3.0)
+    return frameInWindow.midY >= threshold ? .down : .up
+  }
+
   func didGetEmoji(emoji: String) {
     onEmojiSelected([
       "emoji": emoji