[Shell] Add FlyoutIcon (#5567) fixes #4766 fixes #4767 fixes #4845 fixes #5219

[Shell] Add FlyoutIcon  (#5567) fixes #4766 fixes #4767 fixes #4845 fixes #5219

* [Controls]  Add repo for shell issue

* [iOS] Allow specify SetPaddingInsets on the ShellContent

* [iOS,Shell] Fix issue when disposing ToolbarItems  of old page

* [Controls] Add demo repo for #5466

* [Shell,Core] Fix navigating to a registered route

* [Shell,Core] Add better exception messages for wrong or non existing content fixes #5081

* [Core,Shell,iOS,Android] Add FlyoutIcon property

* [Controls] Make shell sample work on Android

* [Controls,Android] Add ImageSource support to FlyoutIcon

* [Android]Allow to set text on the back button

* [Android] Create default text back button

* [Controls] Add example to push with back button behavior

* [Android] Fix back button tint color

* [Android] Cleanup and refactor UpdateDrawerArrow

* Update Xamarin.Forms.Platform.Android/Renderers/ShellToolbarTracker.cs

Co-Authored-By: rmarinho <me@ruimarinho.net>
* [iOS,Shell] Fix go back (Pop) when proving BackButtonBehavior

* [iOS] Check the ParentViewController since we were push to it

* [Android,iOS,Shell] Remove extra code implement feedback

* removed old code

* minor cleanup