4167 [multiple_web] Update web plugin testing instructions. (cla: yes, waiting for tree to go green, p: file_selector, p: google_maps_flutter, p: google_sign_in, p: url_launcher, p: video_player, p: connectivity, platform-web)

4171 [flutter_plugin_tools] Use -version with java (cla: yes, waiting for tree to go green)

4175 [camera_web] Add availableCameras implementation (cla: yes, waiting for tree to go green, p: camera, platform-web)

4178 [webview_flutter] Refactored creation of Android WebView for testability. (cla: yes, waiting for tree to go green, p: webview_flutter, platform-android)

4181 [image_picker] Move UI test (cla: yes, waiting for tree to go green, p: image_picker, platform-ios)