Fix documentation for DlllImportAttribute.PreserveSig (dotnet#5303)

- Note behavior for methods with return value
- Delete references to "retval return value" that did not make sense

Author: jkotas

xml/System.Runtime.InteropServices/DllImportAttribute.xml

@@ -483,16 +483,16 @@
         <ReturnType>System.Boolean</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>Indicates whether unmanaged methods that have <see langword="HRESULT" /> or <see langword="retval" /> return values are directly translated or whether <see langword="HRESULT" /> or <see langword="retval" /> return values are automatically converted to exceptions.</summary>
+        <summary>Indicates whether unmanaged methods that have <see langword="HRESULT" /> return values are directly translated or whether <see langword="HRESULT" /> return values are automatically converted to exceptions.</summary>
         <remarks>
           <format type="text/markdown"><![CDATA[  
   
 ## Remarks  
- Set the <xref:System.Runtime.InteropServices.DllImportAttribute.PreserveSig> field to `true` to directly translate unmanaged signatures with `HRESULT` or `retval` values; set it to `false` to automatically convert `HRESULT` or `retval` values to exceptions. By default, the <xref:System.Runtime.InteropServices.DllImportAttribute.PreserveSig> field is `true`.  
+ Set the <xref:System.Runtime.InteropServices.DllImportAttribute.PreserveSig> field to `true` to translate unmanaged signatures with `HRESULT` values directly; set it to `false` to automatically convert `HRESULT` return values to exceptions. By default, the <xref:System.Runtime.InteropServices.DllImportAttribute.PreserveSig> field is `true`.  
   
- When `true`, the resulting method signature returns an integer value that contains the `HRESULT` value.  In this case, you must manually inspect the return value and respond accordingly in your application.  
+ When `true`, the managed method signature returns an integer value that contains the `HRESULT` value.  In this case, you must manually inspect the return value and respond accordingly in your application.  
   
- When you set the <xref:System.Runtime.InteropServices.DllImportAttribute.PreserveSig> field to `false`, the resulting method signature contains a void return type instead of an integer (`HRESULT`) return type.  When the unmanaged method produces an `HRESULT`, the runtime automatically ignores a return value of `S_OK` (or 0) and does not throw an exception.  For `HRESULT`s other than `S_OK`, the runtime automatically throws an exception that corresponds to the `HRESULT`.  Note that the <xref:System.Runtime.InteropServices.DllImportAttribute> attribute only performs this conversion to methods that return an `HRESULT`.  
+ When you set the <xref:System.Runtime.InteropServices.DllImportAttribute.PreserveSig> field to `false`, the managed method signature has a void return type or the type of the last unmanaged [out, retval] parameter.  When the unmanaged method produces an `HRESULT`, the runtime automatically ignores a return value of `S_OK` (or 0) and does not throw an exception.  For `HRESULT`s other than `S_OK`, the runtime automatically throws an exception that corresponds to the `HRESULT`.
   
  You might decide to change the default error reporting behavior from `HRESULT`s to exceptions in cases where exceptions better fit the error reporting structure of your application.  
   

xml/System.Runtime.InteropServices/PreserveSigAttribute.xml

@@ -48,7 +48,7 @@
     </Attribute>
   </Attributes>
   <Docs>
-    <summary>Indicates that the HRESULT or <see langword="retval" /> signature transformation that takes place during COM interop calls should be suppressed.</summary>
+    <summary>Indicates that the HRESULT signature transformation that takes place during COM interop calls should be suppressed.</summary>
     <remarks>
       <format type="text/markdown"><![CDATA[