`SegmentedItem` should expose `ContentHolder`'s `Margin`

[Lightczx]

Describe the bug

As DefaultSegmentedItemStyle https://github.com/CommunityToolkit/Windows/blob/dec350be1dc1d7d9dda734f0de824d4f030aac35/components/Segmented/src/SegmentedItem/SegmentedItem.xaml#L627-L632

and PivotSegmentedItemStyle https://github.com/CommunityToolkit/Windows/blob/dec350be1dc1d7d9dda734f0de824d4f030aac35/components/Segmented/src/SegmentedItem/SegmentedItem.xaml#L861-L865

the ContentHolder hardcoded it's Margin, but

https://github.com/CommunityToolkit/Windows/blob/dec350be1dc1d7d9dda734f0de824d4f030aac35/components/Segmented/src/SegmentedItem/SegmentedItem.xaml#L1061-L1066

ButtonSegmentedItemStyle using Padding property which come from ButtonItemPadding resource

Expected behavior

Add a new Thickness resource like DefaultSegmentedItemContentPadding, so that we can alter the content padding easily.

Code Platform

• [ ] UWP
• [X] WinAppSDK / WinUI 3
• [ ] Web Assembly (WASM)
• [ ] Android
• [ ] iOS
• [ ] MacOS
• [ ] Linux / GTK

Windows Build Number

• [ ] Windows 10 1809 (Build 17763)
• [ ] Windows 10 1903 (Build 18362)
• [ ] Windows 10 1909 (Build 18363)
• [ ] Windows 10 2004 (Build 19041)
• [ ] Windows 10 20H2 (Build 19042)
• [ ] Windows 10 21H1 (Build 19043)
• [ ] Windows 10 21H2 (Build 19044)
• [ ] Windows 10 22H2 (Build 19045)
• [X] Windows 11 21H2 (Build 22000)
• [ ] Other (specify)

Other Windows Build number

No response

App minimum and target SDK version

• [ ] Windows 10, version 1809 (Build 17763)
• [ ] Windows 10, version 1903 (Build 18362)
• [ ] Windows 10, version 1909 (Build 18363)
• [ ] Windows 10, version 2004 (Build 19041)
• [ ] Windows 10, version 2104 (Build 20348)
• [X] Windows 11, version 22H2 (Build 22000)
• [ ] Other (specify)

Other SDK version

No response

Visual Studio Version

2022

Visual Studio Build Number

No response

Device form factor

Desktop

Additional context

No response

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