[jokerttu]

Summary

Upgrades the native iOS Navigation SDK and Maps SDK from 11.1.0 to 11.3.0, stacked on #784. This PR supersedes #786 and includes its 11.2.0 commit.

• Raise the iOS deployment target to 17.0 in Package.swift, the example app, and the README, as required by SDK 11.3.0.
• Migrate setDestinations to the completionHandler methods; the callback methods are deprecated in 11.3.0. The route-token path uses setDestinationsWithToken:completionHandler:, so waypoints are no longer sent with a route token on iOS.
• Set the travel mode before the route-token call. The SDK rejects the token when the travel mode at call time is unsupported; it was previously set after the call.
• Add RouteStatusUnavailableException, thrown when the native SDK completes a route request without a route status. iOS reports a missing route description; Android guards the unannotated RouteDescription parameter in setDestinations and the simulator wrappers instead of crashing.
• Document that route token routing options take precedence over client-side settings on both platforms (upstream change of 2026-10-23).
• Extend MIGRATING.md with the iOS migration steps.

BREAKING CHANGE: iOS Navigation SDK 11.3.0 requires iOS 17.0 or later and Xcode 26. On iOS, setDestinations with RouteTokenOptions no longer sends waypoints; setDestinations and the Android simulateLocationsAlongNewRoute methods throw RouteStatusUnavailableException when the SDK returns no route status.

See MIGRATING.md for migration instructions.

Partially implements: #782

Checks run

• flutter test: all passing.
• melos run test:ios on iPhone 17 Pro (iOS 26.5): passing, including the new ConvertTests.
• Android unit tests (:google_navigation_flutter:test): passing, including the new missing-route-description test.
• flutter build ios --release --no-codesign and flutter build apk --release: succeed.
• Each new test was confirmed to fail with its guard or error mapping removed.
• Remaining plugin deprecation warnings on iOS are the two terms-and-conditions calls, already deprecated in 11.2.0.
• Patrol tests were not run.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation
• I added new tests to check the change I am making
• All existing and new tests are passing.