SegmentedItem should expose ContentHolder's Margin

[Lightczx]

Describe the bug

As DefaultSegmentedItemStyle

Windows/components/Segmented/src/SegmentedItem/SegmentedItem.xaml

Lines 627 to 632 in dec350b

	<!-- Content -->
	<Grid x:Name="ContentHolder"
	Margin="11,0,11,0"
	HorizontalAlignment="Center"
	VerticalAlignment="Stretch"
	ColumnSpacing="8">

and PivotSegmentedItemStyle

Windows/components/Segmented/src/SegmentedItem/SegmentedItem.xaml

Lines 861 to 865 in dec350b

	<Grid x:Name="ContentHolder"
	Margin="12,0,12,0"
	HorizontalAlignment="Center"
	VerticalAlignment="Stretch"
	ColumnSpacing="8">

the ContentHolder hardcoded it's Margin, but

Windows/components/Segmented/src/SegmentedItem/SegmentedItem.xaml

Lines 1061 to 1066 in dec350b

	<!-- Content -->
	<Grid x:Name="ContentHolder"
	Margin="{TemplateBinding Padding}"
	HorizontalAlignment="Center"
	VerticalAlignment="Stretch"
	ColumnSpacing="8">

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
• 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)
• 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)
• 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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