fix: custom visitor documentation

[mvarendorff]

Description

This PR contains an update to the documentation about custom visitors to make use of oldVisit instead of graphql's visit function which causes issues in graphql@16.

Related #9230

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• This change requires a documentation update

How Has This Been Tested?

Updating this Codesandbox in the same way as the documentation to verify this working.

https://codesandbox.io/p/sandbox/headless-cloud-6z6r45

Test Environment:

• OS: Windows 10
• NodeJS: 16.20.0

Checklist:

• I have followed the CONTRIBUTING doc and the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Further comments

A couple of the checkboxes are left unticked because I am not sure how they apply to pure documentation changes like in this case. Let me know if anything is missing!

[changeset-bot]

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Latest commit: 2ec6970

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[rohit-techolution]

Can we get this sorted ASAP please?

[saihaj]

Thanks