Increases the minimum macOS deployment target from macOS 10.13 (High Sierra) to 10.14 (Mojave) in the macOS app templates.

Includes:
* Update migration for macOS 10.11 apps to upgrade to 10.14
* Adds migration for macOS 10.13 apps to upgrade to 10.14
* Apply migration to all examples, and integration tests

This does not increase version in the plugin templates since those will need to wait until the 10.14 framework rolls to stable channel, so new plugins can build with apps created with `flutter create` on stable channel.

Issue: https://github.com/flutter/flutter/issues/114445
See RFC: http://flutter.dev/go/flutter-drop-macOS-10.13-2022-q4
See previous patch: https://github.com/flutter/flutter/pull/107689