Add CSIDL terminology to Environment.SpecialFolder documentation (#11460)

* Initial plan for issue

* Add CSIDL terminology to Environment.SpecialFolder summary

Co-authored-by: jeffhandley <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: jeffhandley <[email protected]>

Author: Copilot

xml/System/Environment+SpecialFolder.xml

@@ -56,7 +56,7 @@
     </Attribute>
   </Attributes>
   <Docs>
-    <summary>Specifies enumerated constants used to retrieve directory paths to system special folders.</summary>
+    <summary>Specifies enumerated Constant Special Item ID List (CSIDL) values used to retrieve directory paths to system special folders.</summary>
     <remarks>
       <format type="text/markdown"><![CDATA[