[ios] Shell inset, general SafeArea fixes for shell and non shell embedded pages...

[ios] Shell inset,  general SafeArea fixes for shell and non shell embedded pages, entry scrolling fixes (#6457)

* [ios] insets, keyboard scroll, safearea

* ui tests

* small fixes

* ui tests

* additional ui test

* reset default padding more intelligently

* ios10 fixes

* ios10 fixes

* use safe area only if tabbar or navbar is present

* better searching for uiscrollview

* ios11 ui test fixes

* slight delay for scroll to resolve before checking

* Update Xamarin.Forms.Platform.iOS/Renderers/PageRenderer.cs

Co-Authored-By: Pavel Yakovlev <v-payako@microsoft.com>
* Update Xamarin.Forms.Platform.iOS/Renderers/KeyboardInsetTracker.cs

Co-Authored-By: Pavel Yakovlev <v-payako@microsoft.com>
* Update Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/ShellInsets.cs

Co-Authored-By: Pavel Yakovlev <v-payako@microsoft.com>
* try to fix ui tests apply pr suggestions

* more app center ios10 tweaks

* ios 10 fixes

* Update Xamarin.Forms.Platform.iOS/Renderers/ScrollViewRenderer.cs

Co-Authored-By: Pavel Yakovlev <v-payako@microsoft.com>
* Update Xamarin.Forms.Platform.iOS/Renderers/ShellSectionRootRenderer.cs

Co-Authored-By: Pavel Yakovlev <v-payako@microsoft.com>
* PR comments

* fix inset change thrashing and only send offset when changed

* add delay for loading url images and rename shell test

* add null check to extension