[sensors] Update readme documentation (flutter#2452)

Update readme to fix typo in example for user accelerometer event

[sensors] Update readme documentation (flutter#2452)

Update readme to fix typo in example for user accelerometer event

[webview_flutter] always make sure the contentInset or the sum of con…

…tentInset and adjustedContentInset is 0 on iOS. (flutter#2466)

[image_picker] Fix an issue that the example app won't launch the ima…

…ge picker after Android V2 embedding migration. (flutter#2469)

[flutter_plugin_android_lifecycle] Stop reflecting (flutter#2467)

The reflection was added to make the plugin compatible with previous
versions of Flutter. Now that the latest stable has updated we can
update the code to be safer and avoid potential issues with code
shrinking in release builds.

Also removes a Gradle workaround that was only required for pre 1.12
versions of Flutter.

[android_intent] support for setType() and setDataAndType() (flutter#…

…1983)

Added support for [setType](https://developer.android.com/reference/android/content/Intent.html#setType(java.lang.String)) and [setDataAndType](https://developer.android.com/reference/android/content/Intent.html#setDataAndType(android.net.Uri,%20java.lang.String)) parameters. 
This is needed if IE. you want to send intent to stream video. You would need to set both data (some http Uri) and mime type (ie. 'video/*'). Keep in mind, Intent documentation specifies

> To set only the data URI, call setData(). To set only the MIME type, call setType(). If necessary, you can set both explicitly with setDataAndType().
> 
> Caution: If you want to set both the URI and MIME type, do not call setData() and setType() because they each nullify the value of the other. Always use setDataAndType() to set both URI and MIME type.

[webview_flutter] Fix iOS WebView ignoring SafeArea widget and iOS 13…

… WebView scroll indicator showing at random location. (flutter#2343)

[google_sign_in_web] Fix race condition on init. (flutter#2455)

* [google_sign_in_web] Wait for Auth2 to be really ready.

The Auth object that `.init()` returns may not be fully ready by the time
we start calling methods on it; however it has a `.then()` method that
gets called when it is *really* ready to go.

* Add a completer to signal when Auth2 is ready.
* Throw StateError synchronously if .initialized is checked before calling .init()
* Move auth2-dependent init to the `then` method.
  * onSuccess, complete the auth2 ready future.
  * onError, throw a PlatformException. This is normally triggered when
the domain:port of the web app hasn't been whitelisted on the google
sign in console, and things like that. Useful for debugging.
* Update README with latest setup instructions.

[espresso] Adds EspressoFlutter as a first-party plugin (flutter#2369)

* Initial open source release of Espresso bindings for Flutter as a new first-party plugin, espresso.

[camera] Fix crash from changing permissions (flutter#2447)

Our listeners are called for every single permissions change, not just
the first one. This resulted in multiple replies being sent to Dart and
fatal crashes. Change to instead manually keep track of responses and
only respond to the first call.