Add ListItem to podspec

[lyzhan7]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

Continuation of #1939

• There was a suggestion in that PR to create a separate subspec for both TVC/ListItem to depend on rather than having ListItem depend on all of TVC - followed up on that, and also thought it would be cleaner for the shared tokens/enums that both TVC/ListItem use to be in its own folder, but happy to hear thoughts/go back to only the podspec changes
• ListItem depended on TVC's tokens, as well as several enums. There were a couple enums used that weren't defined in the TableViewCellTokenSet file - I saw there were a couple other enums defined in TableViewCellTokenSet, so I just moved all the shared ones into that file - but maybe would make more sense to put all the enums in its own file

Binary change

Not adding/removing any source code, so I don't think this PR should impact binary size - but if there's a reason to run this let me know
(how is our binary size impacted -- see https://github.com/microsoft/fluentui-apple/wiki/Size-Comparison)

Verification

pod lib lint passes. Unfortunately each run of this seemed like it took about 20 minutes. If there's a faster way to validate podspec changes in fluentui-apple let me know!

Microsoft Reviewers: Open in CodeFlow

[mischreiber]

Looks good overall! I'm debating about the name TableViewListShared, but I also don't have a better idea.