Do not reset expanded steps while polling, only extend them

[das7pad]

Closes #905

Hint: Collapsing a step also marks it as "?selected-node".

Previously, any following polling responses would action on the "?selected-node" again and expand the step that was just collapsed. Also, any other steps that were opened in addition to the last "?selected-node" would be collapsed again. When switching stages, all steps would be collapsed again.
Now, steps do not get collapsed eagerly.

Testing done

pipeline {
    agent any

    stages {
        stage('Hello') {
            steps {
                script {
                    for(int i=1; i<=10; i++) {
                        stage("Stage - ${i}") {
                            sh 'for i in 1 2 3; do sleep 1; echo "Slept ${i} times"; done'
                            sh 'for i in 4 5 6; do sleep 1; echo "Slept ${i} times"; done'
                        }
                    }
                }
            }
        }
    }
}

• Select the first stage
• Expand all the steps
• Navigate to the second stage
• Navigate back to the first stage
• See all steps open

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed

[lewisbirks]

I'm finding that if I subsequently close a step, on the next poll it will reopen that step. I don't think this is the intended behaviour

[das7pad]

I'm finding that if I subsequently close a step, on the next poll it will reopen that step. I don't think this is the intended behaviour

Indeed, this is not intuitive. It is logged as a separate bug:

• Step gets re-opened even if manually closed while build is running #822
• A fix for it is in Keep track of collapsed steps and avoid expanding them automatically #903

[lewisbirks]

I'm finding that if I subsequently close a step, on the next poll it will reopen that step. I don't think this is the intended behaviour

Indeed, this is not intuitive. It is logged as a separate bug:

• Step gets re-opened even if manually closed while build is running #822
• A fix for it is in Keep track of collapsed steps and avoid expanding them automatically #903

My bad, forgot to delete this comment after I had seen the other PR

[lewisbirks]

LGTM, thanks for the improvements 🚀