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.ViewModels/ListItemViewModel.cs

@@ -1,146 +0,0 @@
-// Copyright (c) Microsoft Corporation
-// The Microsoft Corporation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System.Diagnostics.CodeAnalysis;
-using Microsoft.CmdPal.UI.ViewModels.Models;
-using Microsoft.CommandPalette.Extensions;
-using Microsoft.CommandPalette.Extensions.Toolkit;
-
-namespace Microsoft.CmdPal.UI.ViewModels;
-
-public partial class ListItemViewModel(IListItem model, WeakReference<IPageContext> context)
-    : CommandItemViewModel(new(model), context)
-{
-    public new ExtensionObject<IListItem> Model { get; } = new(model);
-
-    public List<TagViewModel>? Tags { get; set; }
-
-    // Remember - "observable" properties from the model (via PropChanged)
-    // cannot be marked [ObservableProperty]
-    public bool HasTags => (Tags?.Count ?? 0) > 0;
-
-    public string TextToSuggest { get; private set; } = string.Empty;
-
-    public string Section { get; private set; } = string.Empty;
-
-    public DetailsViewModel? Details { get; private set; }
-
-    [MemberNotNullWhen(true, nameof(Details))]
-    public bool HasDetails => Details != null;
-
-    public override void InitializeProperties()
-    {
-        if (IsInitialized)
-        {
-            return;
-        }
-
-        // This sets IsInitialized = true
-        base.InitializeProperties();
-
-        var li = Model.Unsafe;
-        if (li == null)
-        {
-            return; // throw?
-        }
-
-        UpdateTags(li.Tags);
-
-        TextToSuggest = li.TextToSuggest;
-        Section = li.Section ?? string.Empty;
-        var extensionDetails = li.Details;
-        if (extensionDetails != null)
-        {
-            Details = new(extensionDetails, PageContext);
-            Details.InitializeProperties();
-            UpdateProperty(nameof(Details));
-            UpdateProperty(nameof(HasDetails));
-        }
-
-        UpdateProperty(nameof(TextToSuggest));
-        UpdateProperty(nameof(Section));
-    }
-
-    protected override void FetchProperty(string propertyName)
-    {
-        base.FetchProperty(propertyName);
-
-        var model = this.Model.Unsafe;
-        if (model == null)
-        {
-            return; // throw?
-        }
-
-        switch (propertyName)
-        {
-            case nameof(Tags):
-                UpdateTags(model.Tags);
-                break;
-            case nameof(TextToSuggest):
-                this.TextToSuggest = model.TextToSuggest ?? string.Empty;
-                break;
-            case nameof(Section):
-                this.Section = model.Section ?? string.Empty;
-                break;
-            case nameof(Details):
-                var extensionDetails = model.Details;
-                Details = extensionDetails != null ? new(extensionDetails, PageContext) : null;
-                Details?.InitializeProperties();
-                UpdateProperty(nameof(Details));
-                UpdateProperty(nameof(HasDetails));
-                break;
-        }
-
-        UpdateProperty(propertyName);
-    }
-
-    // TODO: Do we want filters to match descriptions and other properties? Tags, etc... Yes?
-    // TODO: Do we want to save off the score here so we can sort by it in our ListViewModel?
-    public bool MatchesFilter(string filter) => StringMatcher.FuzzySearch(filter, Title).Success || StringMatcher.FuzzySearch(filter, Subtitle).Success;
-
-    public override string ToString() => $"{Name} ListItemViewModel";
-
-    public override bool Equals(object? obj) => obj is ListItemViewModel vm && vm.Model.Equals(this.Model);
-
-    public override int GetHashCode() => Model.GetHashCode();
-
-    private void UpdateTags(ITag[]? newTagsFromModel)
-    {
-        var newTags = newTagsFromModel?.Select(t =>
-        {
-            var vm = new TagViewModel(t, PageContext);
-            vm.InitializeProperties();
-            return vm;
-        })
-            .ToList() ?? [];
-
-        DoOnUiThread(
-            () =>
-            {
-                // Tags being an ObservableCollection instead of a List lead to
-                // many COM exception issues.
-                Tags = new(newTags);
-
-                UpdateProperty(nameof(Tags));
-                UpdateProperty(nameof(HasTags));
-            });
-    }
-
-    protected override void UnsafeCleanup()
-    {
-        base.UnsafeCleanup();
-
-        // Tags don't have event handlers or anything to cleanup
-        Tags?.ForEach(t => t.SafeCleanup());
-        Details?.SafeCleanup();
-
-        var model = Model.Unsafe;
-        if (model != null)
-        {
-            // We don't need to revoke the PropChanged event handler here,
-            // because we are just overriding CommandItem's FetchProperty and
-            // piggy-backing off their PropChanged
-        }
-    }
-}