Extend ListItem to support overrideTokens

[joannaquu]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

Extending ListItem to support .overrideTokens so that consumers can customize tokens.

• Update ListItem so that every time the body runs, the tokenSet will be recreated with the current tokenOverrides
• Update ListItemDemoController_SwiftUI to use the .overrideTokens modifier
  • .overrideTokens requires that listItem be mutable so move this to a separate var.
• Remove the extension in ListItemDemoController
  • This was currently updating the fluent theme for the TableViewCellTokenSet, which reflected in the list item demo controller. Since this is not the "right" way to override list item tokens, let's remove it so consumers don't try this as well.
• Add leadingContentSize as a var in ListItem so that when leadingContentSize changes, we update our tokens that rely on customViewSize.
  • Previously the .leadingContentSize modifier was creating a brand new token set. This meant that any tokens that were overridden would be lost. Now we can ensure that when leadingContentSize, only the tokens dependent on that update.

Binary change

Total increase: 1,344 bytes
Total decrease: -16,168 bytes

File	Before	After	Delta
Total	31,095,248 bytes	31,080,424 bytes	🎉 -14,824 bytes

Full breakdown

File	Before	After	Delta
FocusRingView.o	838,936 bytes	840,280 bytes	⚠️ 1,344 bytes
__.SYMDEF	4,808,816 bytes	4,806,904 bytes	🎉 -1,912 bytes
ListItemModifiers.o	25,856 bytes	20,544 bytes	🎉 -5,312 bytes
ListItem.o	357,984 bytes	349,040 bytes	🎉 -8,944 bytes

Verification

Visual Verification

iOS	visionOS

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

[anandrajeswaran]

Out of curiosity, what's the perf impact observed or expected here? We can't guarantee when body runs so hopefully can guarantee this is dirt cheap?

[mischreiber]

We talked about this offline quite a bit, and yep, token set creation is dirt cheap. We'll work in the future to make it even cheaper, but performance should be totally acceptable right now.