Update iOS Xcode prerequisite checks

scripts/check-ios-prereqs.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [[ -z "${DEVELOPER_DIR:-}" && -d /Applications/Xcode.app/Contents/Developer ]]; then
+  export DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer
+fi
+
+printf 'Developer dir: %s\n' "${DEVELOPER_DIR:-$(xcode-select -p 2>/dev/null || true)}"
+xcodebuild -version
+xcrun simctl list devices available
+swift --version
+
+printf 'iOS prerequisites are available.\n'