4108 Add Basic Junit Tests to some plugins (cla: yes, p: webview_flutter, p: google_sign_in, p: local_auth, p: video_player, p: shared_preferences, platform-android)

4114 [in_app_purchase] Added priceCurrencySymbol to SkuDetailsWrapper (cla: yes, waiting for tree to go green, p: in_app_purchase, platform-android)

4117 [image_picker] Fixed IOException when cache directory is removed (cla: yes, waiting for tree to go green, p: image_picker, platform-android)

4141 [video_player] Update to ExoPlayer 2.14.1 (cla: yes, p: video_player, platform-android)

4147 Fix webview_flutter Android integration tests and add Espresso (cla: yes, waiting for tree to go green, p: webview_flutter, platform-android)