Teach Groovy to recognize `namespace` method in Groovy Stapler views

Example https://github.com/jenkinsci/jenkins/blob/1ecf191f32d8383661ecf9442a3117047dbd1acf/core/src/main/resources/jenkins/tools/GlobalToolConfiguration/index.groovy#L6-L7

If tag library is available as a class, IntelliJ needs to know that the `namespace` method returns an object of the same type as a parameter class.

Start with the example in Jenkins at core/src/main/resources/jenkins/tools/GlobalToolConfiguration/index.groovy, especially lines 6-7, and trace how the IntelliJ Stapler plugin handles Groovy tag libraries. The work is done when IntelliJ recognizes the namespace method and infers its return object type from the parameter class; no plugin file or test is named in the issue.

Written by the indexing model from the issue text.