Move checkbox to the top to allow toggling it using the space bar (the Enter key already defaults to the Finish) button. (#5792)

Move definition of Launch PowerShell checkbox to the top to allow toggling it using the spacebar (the Enter key already defaults to the Finish button).
Reuse product name variable.

assets/Product.wxs

@@ -38,6 +38,9 @@
     <CustomAction Id="LaunchApplication" BinaryKey="WixCA" DllEntry="WixShellExec" Impersonate="yes" />
     <UI>
       <Dialog Id="MyExitDialog" Width="370" Height="270" Title="!(loc.ExitDialog_Title)">
+        <Control Id="LaunchCheckBox" Type="CheckBox" X="10" Y="243" Width="170" Height="17" Property="LAUNCHAPPONEXIT" Hidden="yes" CheckBoxValue="1" Text="Launch $(env.ProductName)">
+          <Condition Action="show">NOT Installed</Condition>
+        </Control>
         <Control Id="Finish" Type="PushButton" X="236" Y="243" Width="56" Height="17" Default="yes" Cancel="yes" Text="!(loc.WixUIFinish)" />
         <Control Id="Cancel" Type="PushButton" X="304" Y="243" Width="56" Height="17" Disabled="yes" Text="!(loc.WixUICancel)" />
         <Control Id="Bitmap" Type="Bitmap" X="0" Y="0" Width="370" Height="234" TabSkip="no" Text="!(loc.ExitDialogBitmap)" />
@@ -46,9 +49,6 @@
         <Control Id="Description" Type="Text" X="135" Y="70" Width="220" Height="20" Transparent="yes" NoPrefix="yes" Text="!(loc.ExitDialogDescription)" />
         <Control Id="Title" Type="Text" X="135" Y="20" Width="220" Height="60" Transparent="yes" NoPrefix="yes" Text="!(loc.ExitDialogTitle)" />
         <!-- Checkbox to allow starting PowerShell after the installation (in UI mode only) -->
-        <Control Id="LaunchCheckBox" Type="CheckBox" X="10" Y="243" Width="170" Height="17" Property="LAUNCHAPPONEXIT" Hidden="yes" CheckBoxValue="1" Text="Launch PowerShell">
-          <Condition Action="show">NOT Installed</Condition>
-        </Control>
       </Dialog>
       <InstallUISequence>
           <Show Dialog="MyExitDialog" OnExit="success" />