Fix Crashing issue with keyboard scrolling iOS

[tj-devel709]

Description of Change

This PR adds some checks so that we don't crash when the an editor/entry is unfocused and the keyboard goes away, but that editor/entry's Window is null. This one is pretty tricky to test so we may just add this now and keep trying on the test.

Issues Fixed

Fixes #28140

[Copilot]

PR Overview

This PR addresses a crash caused by keyboard dismissal when the associated editor/entry's window is null by adding additional null-checks.

• Added responder window null-checks in ViewExtensions.cs.
• Updated the condition in KeyboardAutoManagerScroll.cs to verify that LastScrollView’s window is not null before proceeding with animations.

Reviewed Changes

File	Description
src/Core/src/Platform/iOS/ViewExtensions.cs	Introduces window null-checks in the responder chain to avoid accessing disposed views (note: using "return null;" in a void method could be problematic).
src/Core/src/Platform/iOS/KeyboardAutoManagerScroll.cs	Adjusts the keyboard hiding animation invocation by verifying that LastScrollView is attached to a window.

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

src/Core/src/Platform/iOS/ViewExtensions.cs:772

• Returning null from a method declared with a void return type is a compile error; consider using 'return;' instead or update the method's return type if a null value is intended.

return null;

src/Core/src/Platform/iOS/ViewExtensions.cs:792

• Returning null from a method declared with a void return type is a compile error; consider using 'return;' instead or update the method's return type if a null value is intended.

return null;