Docs: Replace `@returns` tags in JS docs with `@return`.

Per the documentation standards, `@returns` is an unsupported synonym, `@return` should be used instead:
https://make.wordpress.org/core/handbook/best-practices/inline-documentation-standards/javascript/

See #48303.
Built from https://develop.svn.wordpress.org/trunk@46800


git-svn-id: https://core.svn.wordpress.org/trunk@46600 1a063a9b-81f0-0310-95a4-ce76da25c4cd