Add ability to customize TableViewCell separator color

[joannaquu]

Platforms Impacted

• iOS
• macOS

Description of changes

Added ability to customize TableViewCell's separator color. A new token separatorColor was added to TableViewCellTokenSet.

Binary change

Total increase: 7,704 bytes
Total decrease: 0 bytes

File	Before	After	Delta
Total	30,796,008 bytes	30,803,712 bytes	⚠️ 7,704 bytes

Full breakdown

File	Before	After	Delta
TableViewCell.o	805,384 bytes	809,800 bytes	⚠️ 4,416 bytes
TableViewCellTokenSet.o	108,280 bytes	109,984 bytes	⚠️ 1,704 bytes
__.SYMDEF	4,770,960 bytes	4,772,144 bytes	⚠️ 1,184 bytes
PopupMenuItemCell.o	174,072 bytes	174,208 bytes	⚠️ 136 bytes
PersonaCell.o	62,704 bytes	62,832 bytes	⚠️ 128 bytes
BooleanCell.o	89,904 bytes	90,032 bytes	⚠️ 128 bytes
ListActionItem.o	224,808 bytes	224,816 bytes	⚠️ 8 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

[laminesm]

I'd suggest choosing a more drastic override color in the demo like pink so we can see the overridden separator easier since it's a very tiny control.

[alexanderboswell]

we should also update here: https://github.com/microsoft/fluentui-apple/blob/main/ios/FluentUI/List/ListActionItem.swift

[harrieshin]

I'd suggest choosing a more drastic override color in the demo like pink so we can see the overridden separator easier since it's a very tiny control.

not pink. otherwise accessibility vendors will flag our app as not color contrast accessible.

[joannaquu]

we should also update here: https://github.com/microsoft/fluentui-apple/blob/main/ios/FluentUI/List/ListActionItem.swift

Will do in future pr