3324 Merge null-safety plugins (cla: yes)

3326 [camera_platform_interface] Add torch definition to the FlashModes enum  (cla: yes)

3327 [webview_flutter] Migrate to nnbd (cla: yes)

3328 [android_intent] Migrate to nnbd (cla: yes)

3329 [google_sign_in] Migrate to nnbd (cla: yes)

3334 [webview_flutter] Added ‘allowsInlineMediaPlayback’ property (cla: yes)

3335 [camera] Ios support documentation  (cla: yes)

3336 [camera] Added closeCaptureSession() to stopVideoRecording in Java side (cla: yes)