open new tab icon at the top title is not centered correctly

[Emirhan-7274]

Windows Terminal version

1.19.10821.0

Windows build number

10.0.22631.3447

Other Software

No response

Steps to reproduce

its hard to notice it but if you set "Use acrylic material in the tab row" to true it becomes highly noticable

Expected Behavior

open a new tab icon to be centered

Actual Behavior

open a new tab icon is not centered

[zadjii-msft]

Huh, good eye.

Code is somewhere around here:

terminal/src/cascadia/TerminalApp/TabRowControl.xaml

Lines 48 to 70 in 99061ee

	<mux:TabView.TabStripFooter>
	<Grid>
	<!-- Remove this border after WinUI 2.8 -->
	<Border Height="1"
	VerticalAlignment="Bottom"
	Background="{ThemeResource CardStrokeColorDefaultBrush}" />
	<mux:SplitButton x:Name="NewTabButton"
	x:Uid="NewTabSplitButton"
	Height="24"
	Margin="0,4"
	Padding="0"
	HorizontalAlignment="Left"
	VerticalAlignment="Stretch"
	AllowDrop="True"
	AutomationProperties.AccessibilityView="Control"
	BorderThickness="0"
	Click="OnNewTabButtonClick"
	Content="&#xE710;"
	DragOver="OnNewTabButtonDragOver"
	Drop="OnNewTabButtonDrop"
	FontFamily="{ThemeResource SymbolThemeFontFamily}"
	FontSize="12">

IIRC we're adding some margin to make the + centered nicely, but that code hasn't been touched in years so I may be off base on that