Fix command palette accessibility (#9143)

Fixes a regression of command palette accessibility. The regression was
introduced in #8377 by setting `IsTabStop` to false. Though the commands
would light up, the focus didn't technically get on the command, so the
screen reader would just read the text box.

Opened the command palette while NVDA is active. It now reads the
commands as focus moves on them.

(cherry picked from commit ac3e4bf)

src/cascadia/TerminalApp/CommandPalette.xaml

@@ -285,7 +285,6 @@ the MIT License. See LICENSE in the project root for license information. -->
                         <!-- This HorizontalContentAlignment="Stretch" is important
                         to make sure it takes the entire width of the line -->
                         <ListViewItem HorizontalContentAlignment="Stretch"
-                                  IsTabStop="False"
                                   AutomationProperties.Name="{x:Bind Item.Name, Mode=OneWay}"
                                   AutomationProperties.AcceleratorKey="{x:Bind Item.KeyChordText, Mode=OneWay}">