helper and viewer-level access to data_labels properties

[kecnry]

Description

This pull request implements viz.data_labels, viz.viewers[...].data_labels_loaded, and viz.viewers[...].data_labels_visible which are each a read-only list. This is intended to provide an alternative to suggesting users access viz.app.data_collection to inspect the list of data labels eligible to be passed to viz.get_data(), etc.

In the future, viz.viewer[...].data_labels as a list of all data entries supported by a specific viewer (those loaded as well as those in the expanded data menu) would be convenient, but currently all that logic lives in vue, not python.

See spacetelescope/jdat_notebooks#203 for how this would allow us to remove non-public API from public-facing notebook examples.

Change log entry

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

Checklist for package maintainer(s)

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• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
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[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (8128788) 91.53% compared to head (8a9dfdf) 91.52%.
Report is 10 commits behind head on main.

Files	Patch %	Lines
jdaviz/core/template_mixin.py	69.23%	4 Missing ⚠️
jdaviz/configs/default/plugins/viewers.py	86.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2626      +/-   ##
==========================================
- Coverage   91.53%   91.52%   -0.01%     
==========================================
  Files         161      161              
  Lines       19944    19983      +39     
==========================================
+ Hits        18256    18290      +34     
- Misses       1688     1693       +5     

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[pllim]

Philosophical questions posted, as you requested. 🧐

[pllim]

Hmm...

1. Does this include Mosviz table viewer? Do we want to expose these for Mosviz?
2. How do you want the Imviz fake WCS layers to behave for this? Are they not exposed here even though people can see them in the Data drop down?
3. I am guessing for Cubeviz case, the spectrum viewer will say it has no data labels even though a spectrum is visible because of the collapse magic?

[kecnry]

Does this include Mosviz table viewer? Do we want to expose these for Mosviz?

Good point, I'll exclude from the user-API for table viewers

How do you want the Imviz fake WCS layers to behave for this? Are they not exposed here even though people can see them in the Data drop down?

Good question, they will show up here , and maybe we will want to exclude them. If that's what we want, I can do a follow-up PR to the image rotation PR once its rebased on this or merged into main.

I am guessing for Cubeviz case, the spectrum viewer will say it has no data labels even though a spectrum is visible because of the collapse magic?

No, the spectrum should still show up as it is a data layer loaded into that viewer.

[kecnry]

Excluded now from mosviz, and confirmed that the cube shows up as expected in the spectrum viewer (and matching the UI as of #2631).

I also cross linked back here from the image rotation PR so that we can consider your second question then.

[pllim]

LGTM. Thanks!

[haticekaratay]

I tested the implementation in Imviz and confirmed that it performs as expected. Thanks for your work!