[webview_flutter] Suppress iOS 9 deprecation warnings (flutter#4100)

On master the project is auto-updated to iOS 9, causing CI failures on
this deprecation warning (due to -Werrror), but still needs to support
iOS 8 for current stable.

[image_picker] Updated pickImage and pickVideo docs to expose the pos…

…sible errors that can be thrown (flutter#4089)

[in_app_purchase] Update readme.md (flutter#4049)

Fixed typos and bumped version (flutter#4050)

[in_app_purchase] billingClient launchPriceChangeConfirmationFlow (fl…

…utter#4077)

[image_picker] Multiple image support (flutter#3783)

[in_app_purchase_android] fix version for 'add payment proxy': pull/4…

…055 (flutter#4071)

[in_app_purchase] Added BillingClient.isFeatureSupported (flutter#4063)

* Added BillingClient.isFeatureSupported

* pubspec and changelog

[in_app_purchase_platform_interface] Fixed restoring purchases link (f…

…lutter#4051)

[image_picker] Migrate README example to null-safety (flutter#4038)