* Use FQCN for native attributes
For attributes, it's non-obvious that they need to be imported with `use` or
referenced with their FQCN, because applying a non-existent attribute is not an
error.
Make the examples copy-and-paste safe by adding the leading backslash, as
already done for `#[\SensitiveParameterValue]`.
Tim Düsterhus
6e69d9342e