Corrected note in DllImportResolver (#11865)

Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com>
Co-authored-by: Aaron Robinson <arobins@microsoft.com>
Co-authored-by: Jan Kotas <jkotas@microsoft.com>

Author: 4 people

xml/System.Runtime.InteropServices/DllImportResolver.xml

@@ -39,7 +39,7 @@
 
 The runtime does not do any lifetime management around the handle returned by a <xref:System.Runtime.InteropServices.DllImportResolver>. It is left to the implementation and consuming code to keep the library loaded for as long as necessary and free it if/when desired. 
 
-The resolver delegate is called everytime when a PInvoke call is done. It is fine to cache the handle, as long as the consuming code does not call <xref:System.Runtime.InteropServices.NativeLibrary.Free>.
+The resolver is typically called once for each PInvoke entry point. To improve performance, the implementation of the resolver can cache the `libraryName` to handle mapping, as long as the library isn't unloaded via <xref:System.Runtime.InteropServices.NativeLibrary.Free(System.IntPtr)>.
 
       ]]></format>
     </remarks>