3902 [url_launcher] Migrate maven repo from jcenter to mavenCentral (cla: yes, waiting for tree to go green, p: url_launcher, platform-android)

3903 Enable web integration tests on stable (cla: yes, waiting for tree to go green, p: file_selector, p: google_sign_in, p: url_launcher, p: connectivity, platform-web)

3904 [android_alarm_manager] Migrate maven repo from jcenter to mavenCentral (cla: yes, waiting for tree to go green, p: android_alarm_manager, platform-android)

3905 [path_provider] Migrate all integration tests to NNBD (cla: yes, waiting for tree to go green, p: path_provider, platform-windows, platform-macos, platform-linux)