Create a Microsoft.CmdPal.Core.ViewModels project (#40560)

_targets #40504_ 

Major refactoring for #40113

This moves a large swath of the codebase to a `.Core` project. "Core"
doesn't have any explicit dependencies on "extensions", settings or the
current `MainListPage`. It's just a filterable list of stuff. This
should let us make this component a bit more reusable.

This is half of a PR. As I did this, I noticed a particular bit of code
for TopLevelVViewModels and CommandPaletteHost that was _very rough_.
Solving it in this PR would make "move everything to a new project" much
harder to review. So I'm submitting two PRs simultaneously, so we can
see the changes separately, then merge together.

src/modules/cmdpal/Microsoft.CmdPal.UI/ExtViews/ListPage.xaml

@@ -5,6 +5,7 @@
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:controls="using:CommunityToolkit.WinUI.Controls"
     xmlns:converters="using:CommunityToolkit.WinUI.Converters"
+    xmlns:coreViewModels="using:Microsoft.CmdPal.Core.ViewModels"
     xmlns:cpcontrols="using:Microsoft.CmdPal.UI.Controls"
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:help="using:Microsoft.CmdPal.UI.Helpers"
@@ -27,7 +28,7 @@
             EmptyValue="Collapsed"
             NotEmptyValue="Visible" />
 
-        <DataTemplate x:Key="TagTemplate" x:DataType="viewModels:TagViewModel">
+        <DataTemplate x:Key="TagTemplate" x:DataType="coreViewModels:TagViewModel">
             <cpcontrols:Tag
                 AutomationProperties.Name="{x:Bind Text, Mode=OneWay}"
                 BackgroundColor="{x:Bind Background, Mode=OneWay}"
@@ -39,7 +40,7 @@
         </DataTemplate>
 
         <!--  https://learn.microsoft.com/windows/apps/design/controls/itemsview#specify-the-look-of-the-items  -->
-        <DataTemplate x:Key="ListItemViewModelTemplate" x:DataType="viewModels:ListItemViewModel">
+        <DataTemplate x:Key="ListItemViewModelTemplate" x:DataType="coreViewModels:ListItemViewModel">
             <Grid
                 Padding="0,12,0,12"
                 AutomationProperties.Name="{x:Bind Title, Mode=OneWay}"