Merge "[Thread] add demoapp for Thread network APIs" into main

thread/demoapp/Android.bp

thread/demoapp/AndroidManifest.xml

...roid/threadnetwork/demoapp/ConnectivityToolsFragment.java

.../java/com/android/threadnetwork/demoapp/MainActivity.java

.../threadnetwork/demoapp/ThreadNetworkSettingsFragment.java

...etwork/demoapp/concurrent/BackgroundExecutorProvider.java

thread/demoapp/res/drawable/ic_launcher_foreground.xml

thread/demoapp/res/drawable/ic_menu_24dp.xml

thread/demoapp/res/drawable/ic_thread_wordmark.xml

thread/demoapp/res/layout/connectivity_tools_fragment.xml

thread/demoapp/res/layout/list_server_ip_address_view.xml

thread/demoapp/res/layout/list_server_port_view.xml

thread/demoapp/res/layout/main_activity.xml

thread/demoapp/res/layout/nav_header.xml

...d/demoapp/res/layout/thread_network_settings_fragment.xml

thread/demoapp/res/menu/nav_menu.xml

thread/demoapp/res/mipmap-anydpi-v26/ic_launcher.xml

thread/demoapp/res/mipmap-anydpi-v26/ic_launcher_round.xml

thread/demoapp/res/mipmap-hdpi/ic_launcher.png

thread/demoapp/res/mipmap-hdpi/ic_launcher_round.png