3864 Check in macOS example Podfiles (cla: yes, p: integration_test, p: path_provider, p: url_launcher, p: package_info, p: shared_preferences, p: connectivity, platform-macos)

3923 [shared_preferences] Migrate maven repo from jcenter to mavenCentral (cla: yes, waiting for tree to go green, p: shared_preferences, platform-android)