Fix incorrect data node rendering for modular pipelines

[rashidakanchwala]

Description

Fixes #1123

Development notes

The viz flowchart is actually a representation of modular pipelines. The root modular pipeline is the first thing we see in the collapsed flowchart. It must include:

• All top-level modular pipelines (e.g., level1.node, not level2.level1.node).
• Any tasks, datasets, or parameters not part of a modular pipeline.
• Inputs and outputs to the top-level modular pipeline (also called external_inputs and external_outputs in the code).
• Lastly, all parameters, even if they belong to nested modular pipelines. The flowchart design ensures these parameters remain visible from the root modular pipeline, even when we expand the view.

In the code, there was a variable named root_children_ids, which was causing issues as reported by users. It's a bit confusing what it does but removing it resulted in the parameters not being shown at the root level anymore.

To address this, the variable root_children_ids has been renamed to root_parameters, and it has been modified to include all parameters that are part of a modular pipeline.

After making this change, the code correctly satisfies the above four conditions, ensuring all relevant components are present in the root modular pipeline.

The dummy project the original user posted in the original issue available on box. Please ping me for the link to it

QA notes

Checklist

• Read the contributing guidelines
• Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• Updated the documentation to reflect the code changes
• Added new entries to the RELEASE.md file
• Added tests to cover my changes

[merelcht]

The code looks good to me 👍 Maybe add this to the release notes?

[merelcht]

So was part of the problem that the expected_modular_pipelines in this test wasn't actually correct?

[rashidakanchwala]

This is the part that is weird.
In unit tests parameters that are within a modular pipeline were not showing up in 'root' but in the demo project they were. And as discussed design wise this was what was decided and also made sense. So I had to update this unit test to not only include paramters that are at top-level (f1f1425b) but also parameters that are part of a modular pipeline (f0ebef01)

[tynandebold]

Code looks good.

I couldn't actually test the UI locally with the basic_spaceflights project you provided, as I keep getting this warning even after installing your local branch of the package.

WARNING: You are using an old version of Kedro Viz. You are using version 4.7.1; however, version 6.3.4 is now available.

If you can provide further clarity on how to test that would be great.