Enable xamltools preview by default

Author: dibarbet

package.json

@@ -1722,7 +1722,7 @@
           "dotnet.enableXamlToolsPreview": {
             "scope": "machine-overridable",
             "type": "boolean",
-            "default": false,
+            "default": true,
             "description": "%configuration.dotnet.enableXamlToolsPreview%"
           },
           "dotnet.projects.binaryLogPath": {