[TwoLineTitleViewDemoController] Fix demo crash for iOS 26.* and macCatalyst 26.*

[nodes11]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

The TwoLineTitleViewDemoController crashes on open due to a preconditionFailure "A title image and a subtitle must be provided when isTitleImageLeadingForTitleAndSubtitle is set to true." in the TwoLineTitleView.setup(...) function.

Add an available check in calls the makeExampleNavigationItem so that we set the UINavigationItem.subtitle field for devices running an OS >= 26 and the fluentConfiguration.subtitle for an OS < 26.

Add XCUITest case for this demo controller.

Binary change

(how is our binary size impacted -- see https://github.com/microsoft/fluentui-apple/wiki/Size-Comparison)

Verification

I validated that the demo controller no longer crashes on open and that the subtitles appear as expected.

Visual Verification

Before	After
Screenshot or description before this change	Screenshot or description with this change

Pull request checklist

This PR has considered:

• Light and Dark appearances
• iOS supported versions (all major versions greater than or equal current target deployment version)
• VoiceOver and Keyboard Accessibility
• Internationalization and Right to Left layouts
• Different resolutions (1x, 2x, 3x)
• Size classes and window sizes (iPhone vs iPad, notched devices, multitasking, different window sizes, etc)
• iPad Pointer interaction
• SwiftUI consumption (validation or new demo scenarios needed)
• Objective-C exposure (provide it only if needed)

Microsoft Reviewers: Open in CodeFlow

[joannaquu]

rip our xcuitests should have caught this...

[joannaquu]

rip our xcuitests should have caught this...

oh wait two line title view doesn't have one. can we bundle one in with your change? should just be able to copy paste

fluentui-apple/Demos/FluentUIDemo_iOS/FluentUIDemoTests/ButtonTest.swift

Line 8 in 98f0f2b

class ButtonTest: BaseTest {