use .yml files instead of .xml

Author: gewarren

docfx.json

@@ -147,16 +147,16 @@
         "api/**.yml": ["csharp", "vb", "fsharp", "cpp"]
       },
       "open_to_public_contributors": {
-        "xml/Microsoft.Extensions*/*.xml": false,
-        "xml/System.Composition/*.xml": false,
-        "xml/System.Formats.Cbor/*.xml": false,
-        "xml/System.Formats.Nrbf/*.xml": false,
-        "xml/System.Net.ServerSentEvents/*.xml": false,
-        "xml/System.Numerics.Tensors/*.xml": false,
-        "xml/System.Runtime.Serialization/ISerializationCodeDomSurrogateProvider.xml": false,
-        "xml/System.Runtime.Serialization/ImportOptions.xml": false,
-        "xml/System.Runtime.Serialization/XsdDataContractExporter.xml": false,
-        "xml/System.Speech*/*.xml": false
+        "xml/Microsoft.Extensions*/*": false,
+        "xml/System.Composition/*": false,
+        "xml/System.Formats.Cbor/*": false,
+        "xml/System.Formats.Nrbf/*": false,
+        "xml/System.Net.ServerSentEvents/*": false,
+        "xml/System.Numerics.Tensors/*": false,
+        "xml/System.Runtime.Serialization/ISerializationCodeDomSurrogateProvider.yml": false,
+        "xml/System.Runtime.Serialization/ImportOptions.yml": false,
+        "xml/System.Runtime.Serialization/XsdDataContractExporter.yml": false,
+        "xml/System.Speech*/*": false
       }
     },
     "dest": "_site",