[EnvVar][Hosts][RegPrev]Decouple and refactor to make it "packable" as nuget package (#32604)

* WIP Hosts - remove deps

* Add consumer app

* Move App and MainWindow to Consumer app. Make Hosts dll

* Try consume it

* Fix errors

* Make it work with custom build targets

* Dependency injection
Refactor
Explicit page creation
Wire missing dependencies

* Fix installer

* Remove unneeded stuff

* Fix build again

* Extract UI and logic from MainWindow to RegistryPreviewMainPage

* Convert to lib
Change namespace to RegistryPreviewUILib
Remove PT deps

* Add exe app and move App.xaml and MainWindow.xaml

* Consume the lib

* Update Hosts package creation

* Fix RegistryPreview package creation

* Rename RegistryPreviewUI back to RegistryPreview

* Back to consuming lib

* Ship icons and assets in nuget packages

* Rename to EnvironmentVariablesUILib and convert to lib

* Add app and consume

* Telemetry

* GPO

* nuget

* Rename HostsPackageConsumer to Hosts and Hosts lib to HostsUILib

* Assets cleanup

* nuget struct

* v0

* assets

* [Hosts] Re-add AppList to Lib Assets, [RegPrev] Copy lib assets to out dir

* Sign UI dlls

* Revert WinUIEx bump

* Cleanup

* Align deps

* version exception dll

* Fix RegistryPreview crashes

* XAML format

* XAML format 2

* Pack .pri files in lib/ dir

---------

Co-authored-by: Darshak Bhatti <dabhatti@microsoft.com>

src/modules/Hosts/HostsUILib/Settings/HostsAdditionalLinesPosition.cs

@@ -0,0 +1,12 @@
+// 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.
+
+namespace HostsUILib.Settings
+{
+    public enum HostsAdditionalLinesPosition
+    {
+        Top = 0,
+        Bottom = 1,
+    }
+}

src/modules/Hosts/HostsUILib/Settings/HostsEncoding.cs

@@ -0,0 +1,12 @@
+// 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.
+
+namespace HostsUILib.Settings
+{
+    public enum HostsEncoding
+    {
+        Utf8 = 0,
+        Utf8Bom = 1,
+    }
+}

src/modules/Hosts/HostsUILib/Settings/IUserSettings.cs

@@ -0,0 +1,24 @@
+// 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;
+using System.Net;
+
+namespace HostsUILib.Settings
+{
+    public interface IUserSettings
+    {
+        public bool ShowStartupWarning { get; }
+
+        public bool LoopbackDuplicates { get; }
+
+        public HostsAdditionalLinesPosition AdditionalLinesPosition { get; }
+
+        public HostsEncoding Encoding { get; }
+
+        event EventHandler LoopbackDuplicatesChanged;
+
+        public delegate void OpenSettingsFunction();
+    }
+}