Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

DESCRIPTION

• Adds an opt-in Blur Effect background for the BottomSheet Contro
• Add UIBlurEffect support to the BottomSheet by using a UIVisualEffectsView.
• Add an optional usesBlurEffectBackground to BottomSheetController and BottomCommandingController initializers, to opt into this new effect.
• Also account for a ShadowEffect which needs a special case handling for UIVisualEffectsView shadows, which would need a different logic from that currently implemented in Fluent Shadow API ShadowInfo:applyShadow:to:. This applyShadow API adds additional CALayers (configured with shadow properties) as shadow layers to the View essentially relying on the view having an opaque backgroundColor for the shadow to show (the opacity of the backgroundColor is directly proportional to the shadow opacity). But when using a UIVisualEffectsView, we can't set an opaque backgroundColor, as it would obstruct the content blurring/sampling feature of this special effects view and would defeat the purpose of using it entirely. So directly add the Shadow tokens to the UIVisualEffectsView layer.

Verification

• Tested locally by opting into the usesBlurEffectBackground by doing a let bottomCommandingVC = BottomCommandingController(with: optionTableViewController, usesBlurEffectBackgroundForBottomSheet: true) in the corresponding demo controller.
• The default behavior is unaffected. ie. uses opaque background.

Visual Verification (NOTE: very subtle difference - there's a blue color bleed through under the Mode button

Before	After

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)