Fix crash on disabled TitleBarPaneToggleButton style

[Zakariathr22]

Fixes

• Fixes Cannot find a Resource with the Name/Key TitleBarPaneToggleButtonForegroundDisabled #10739

PR Type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

Description

Fixes a crash when disabling the TitleBarPaneToggleButtonStyle.
The crash was caused by a storyboard targeting an invalid property (Background on AnimatedIcon) and by the absence of a TitleBarPaneToggleButtonForegroundDisabled resource.

Current Behavior

• Disabling a button with the style causes the app to crash.
• Crash occurs because AnimatedIcon does not support Background, and the style references a missing resource.

New Behavior

• Storyboard now targets RootGrid.Background instead of AnimatedIcon.Background.
• A new resource TitleBarPaneToggleButtonForegroundDisabled has been added.
• Button disables gracefully without crashing, with proper visual feedback.

Motivation and Context

This change prevents application crashes when the button is disabled.

How Has This Been Tested?

• I have performed a self-review of my own code
• I have added tests to cover my changes

Screenshots (if appropriate):

[beth-panx]

Hey @Zakariathr22 - I am mirroring your changes in the internal repo and adding tests for it too. This will be added to the next release. Does that sound good?

[Zakariathr22]

Hey @Zakariathr22 - I am mirroring your changes in the internal repo and adding tests for it too. This will be added to the next release. Does that sound good?

Sounds good 👍