Add docs for AdaptationConstants (#2808)

* Add docs for AdaptationConstants APIs

* Update xml/System.ComponentModel.Composition/AdaptationConstants.xml

Co-Authored-By: Maira Wenzel <mairaw@microsoft.com>

Author: maryamariyan

xml/System.ComponentModel.Composition/AdaptationConstants.xml

@@ -14,7 +14,7 @@
   </Base>
   <Interfaces />
   <Docs>
-    <summary>To be added.</summary>
+    <summary>Contains static metadata keys used by the composition system.</summary>
     <remarks>To be added.</remarks>
   </Docs>
   <Members>
@@ -34,7 +34,7 @@
         <ReturnType>System.String</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
+        <summary>Specifies the contract name for an adapter.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -54,7 +54,7 @@
         <ReturnType>System.String</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
+        <summary>Specifies the metadata key created by the composition system to mark an adapter from a contract.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -74,9 +74,9 @@
         <ReturnType>System.String</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
+        <summary>Specifies the metadata key created by the composition system to mark an adapter to a contract.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
   </Members>
-</Type>
+</Type>