Standardizing built-in extension icon handling (#40606)

Just standardizing built-in extensions to use a `internal sealed class
Icons` for all their non-dynamic icons.

Looks like a LOT of changes, but it's icons all the way down.

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.WindowWalker/Components/ResultHelper.cs

@@ -119,7 +119,7 @@ internal static class ResultHelper
         return new WindowWalkerListItem(null)
         {
             Title = Resources.windowwalker_ExplorerInfoTitle,
-            Icon = new IconInfo("\uE946"), // Info
+            Icon = Icons.Info,
             Subtitle = Resources.windowwalker_ExplorerInfoSubTitle,
             Command = new ExplorerInfoResultCommand(),
         };