[JENKINS-74026][JENKINS-74027] Improve CSP compatibility

[yaroslavafenkin]

• Extract inline JavaScript from DynamicReferenceParameter/index.jelly
• Extract inline JavaScript from CascadeChoiceParameter/index.jelly

https://issues.jenkins.io/browse/JENKINS-74026
https://issues.jenkins.io/browse/JENKINS-74027

Testing done

I've relied a lot on the scenario from https://issues.jenkins.io/browse/JENKINS-71909. Made sure that isn't broken. Unit test that asserts that behavior is very much appreciated, helped me a lot along the way. I feel like I'm almost over relying on it though.

Before the fix
After the fix

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 demonstrates feature works or fixes the issue

[yaroslavafenkin]

While working on fixing https://issues.jenkins.io/browse/JENKINS-74026 individually I realized it makes more sense to fix both issues together since I'll apply the same approach for both of them. Videos with explanations do not cover that part of the fix. It has been tested manually the same way, I've just changed the last parameter from Active Choices Reactive Parameter to Active Choices Reactive Reference Parameter.

[yaroslavafenkin]

Never a null when saved via UI.