AK: Rename adopt() to adopt_ref()

This makes it more symmetrical with adopt_own() (which is used to
create a NonnullOwnPtr from the result of a naked new.)

Userland/DevTools/HackStudio/FindInFilesWidget.cpp

@@ -110,7 +110,7 @@ static RefPtr<SearchResultsModel> find_in_files(const StringView& text)
         }
     });
 
-    return adopt(*new SearchResultsModel(move(matches)));
+    return adopt_ref(*new SearchResultsModel(move(matches)));
 }
 
 FindInFilesWidget::FindInFilesWidget()