* 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]`.
We require suitable return types or the ReturnTypeWillChange attribute
as of PHP 8.1.0. We specify the return types where supported as of PHP
7.0.0, but go with the attribute for the union types.
Cf. <https://github.com/php/doc-en/issues/1090>.
Instead of actually adding proper input validation to the example,
we prominently note that this would have to be done for production
code.
git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@342943 c90b9560-bf6c-de11-be94-00142212c4b1
