[CommandBar] Add Glass Styling Support

[cbowdoin]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

Introduces a new CommmandBarStyle .primary and .glass to style the CommandBar using UIGlassEffect on iOS26 and UIBlurEffect on older OS. The styling also adjust the shadows to match the glass style.

Change also includes a minor bug fix to the corner radius calculation so we get full half circles in command bars that try and layout below the safe area which previously could be seen in the DemoController Accessaory Input View when the soft keyboard was not showing

Binary change

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

Verification

(how the change was tested, including both manual and automated tests)

Visual Verification

Before	After

Pull request checklist

This PR has considered:

• iOS supported versions (all major versions greater than or equal current target deployment version)
• Size classes and window sizes (iPhone vs iPad, notched devices, multitasking, different window sizes, etc)
• Objective-C exposure (provide it only if needed)

Microsoft Reviewers: Open in CodeFlow