Fixed [iOS] Navigation breaks when modal pages use PageSheet

[NanthiniMahalingam]

Issue Details

• The NavigationPage does not push the modal page using the PushModalAsync method after using the PageSheet.

Root Cause

• The NavigationPage's view controller UIView window is null when using PageSheet, preventing the modal page from being presented in the view.

Description Changes

• Added a null check condition for the view controller's ViewIfLoaded window and obtained the modal navigation page wrapper view from the window's root view controller.

Issues Fixed

Fixes #27670

Validated the behaviour in the following platforms

• [] Android
• [] Windows
• iOS
• [] Mac

Output

iOS platform

Before	After
27670_Before.mp4	27670_After.mp4

[dotnet-policy-service]

Hey there @NanthiniMahalingam! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[jsuarezruiz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[haavamoa]

Awesome job! When will this be released?

[haavamoa]

This is not fixed in 9.0.50 SR5, created a new issue:
#28444