[PHP] map AnyType to mixed

[wing328]

To fix #6668

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project beforehand.
• Run the shell script ./bin/generate-samples.shto update all Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/config/java*. For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

cc @jebentier (2017/07), @dkarlovi (2017/07), @mandrean (2017/08), @jfastnacht (2017/09), @ackintosh (2017/09) ❤️, @ybelenko (2018/07), @renepardon (2018/12)

[ybelenko]

Are you sure it won't break anything? mixed is pseudotype which works only in doc block comments.

function foobar(mixed $var) {}
// crashes cause unknown mixed class
function foobar(): mixed {}
// crashes too

[wing328]

    public function deletePetWithHttpInfo($pet_id, $api_key = null)

That's an example of the method signature in the PHP client. I don't see the type (mixed in the example you provided above) included in the method signature. I've not reviewed all auto-generated PHP code (e.g. from PHP Symfony server generator) though.

To answer your question, I'm aware mixed is used in the documentation only and I'm not sure if it will cause issues in our case. That's why I tagged the PHP technical committee for review.

If you've better suggestions on what AnyType should be mapped to, please feel free to suggest.

[ybelenko]

I didn't checked it locally with PHP generators, but I think there will be no syntax errors. I hope so 😄