Add ability to customize SideTabBar's background and separator color

[joannaquu]

Platforms Impacted

• iOS
• macOS

Description of changes

Added ability to customize SideTabBar's background and separator color. Two new tokens, backgroundColor and separatorColor were added to SideTabBarTokenSet. Also fixed some comments/whitespace.

Binary change

Total increase: 52,136 bytes
Total decrease: -30,184 bytes

File	Before	After	Delta
Total	30,900,632 bytes	30,922,584 bytes	⚠️ 21,952 bytes

Full breakdown

File	Before	After	Delta
FluentTheme.o	154,904 bytes	197,472 bytes	⚠️ 42,568 bytes
SideTabBar.o	199,568 bytes	205,704 bytes	⚠️ 6,136 bytes
SideTabBarTokenSet.o	49,848 bytes	52,632 bytes	⚠️ 2,784 bytes
FocusRingView.o	814,384 bytes	815,032 bytes	⚠️ 648 bytes
__.SYMDEF	4,777,304 bytes	4,775,368 bytes	🎉 -1,936 bytes
FluentUIFramework.o	104,616 bytes	76,368 bytes	🎉 -28,248 bytes

Verification

Visual Verification

Light	Dark

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