Added onEnterRules for the following cases:

```xaml
<Button>|</Button>
=>
<Button>
    |
</Button>
```

and

```xaml
<Button Width="100" |
=>
<Button Width="100"
    |
```

Everything else will get the previous indent as before.

Author: mgoertz-msft

src/xaml/language-configuration.json

@@ -55,5 +55,20 @@
 	},
 	"wordPattern": {
 		"pattern": "(-?\\d*\\.\\d\\w*)|([^\\`\\~\\!\\@\\#\\$\\%\\^\\&\\*\\(\\)\\=\\+\\[\\{\\]\\}\\\\\\|\\;\\:\\'\\\"\\,\\.\\<\\>\\/\\?\\s]+)"
-	}
+	},
+  "onEnterRules": [
+    {
+      "beforeText": "^\\s*(<([A-Za-z0-9_.-]+)([^/>]*(?!/)>)[^<]*)(?!.*<\\/\\2>)$",
+      "afterText": "^\\s*<\\/([A-Za-z0-9_.-]+)[^>]*>$",
+      "action": {
+        "indent": "indentOutdent"
+      }
+    },
+    {
+      "beforeText": "^\\s*(<([A-Za-z0-9_.-]+)[^</]*)$",
+      "action": {
+        "indent": "indent"
+      }
+    },
+  ]
 }