[fxcop] Settings UI library (part 1) (#7187)

* Mark methods static and replace Count() with Length

* Use IsNullOrEmpty for null string checks

* Remove redundant initializations to default values

* Use nameof(property name) in place of string literals

* Add NativeMethods class

* Rename property getters in KeysDataModel & AppSpecificKeysDataModel

* Remove underscores from method names

* Mark Helper class static

* Address comments & typo fixes

* Add EncoderGuid property and fix failing build

* Update binding in GeneralPages.xaml

src/core/Microsoft.PowerToys.Settings.UI/Views/GeneralPage.xaml

@@ -125,7 +125,7 @@
             <Button x:Uid="GeneralPage_CheckForUpdates"
                     Style="{StaticResource AccentButtonStyle}"
                     Foreground="White"
-                    Command="{Binding CheckFoUpdatesEventHandler}"
+                    Command="{Binding CheckForUpdatesEventHandler}"
                     />
 
             <ToggleSwitch x:Uid="GeneralPage_ToggleSwitch_AutoDownloadUpdates"