refactors status-indicator imgs and related elements for ARIA labeling

[cfm]

Status

Ready for review

Description of Changes

Resolves #5985.

This PR builds on #5996 to make more-meaningful use of both alt attributes (on img elements) and aria-* annotations (on img and other elements) in those cases where an image indicates the status of another UI element. These images are not strictly decorative, but nor is their UI role communicated (and narrated by screen-readers) from functional markup such as button elements. Instead, this more-nuanced refactoring (a) simplifies the existing markup (and narration) and (b) establishes narratable relationships between elements.

This PR (especially cbff6b9) can be thought of as the prototype for the top-down semantic refactoring proposed in #5986 and #5987.

Testing

With a screen-reader running:

1. Journalist Interface → log in as a journalist: Observe that a source's "star" button, un/starred status, selection checkbox, and link are announced separately and logically, before the other information in the row.
2. Journalist Interface → log in as a journalist → select a source: Observe that a document's name, un/read status, and type are announced together; followed by its selection checkbox; followed by the other information in the row.

Deployment

No special considerations.

Checklist

If you made changes to the server application code:

• Linting (make lint) and tests (make test) pass in the development container

[codecov-commenter]

Codecov Report

Merging #6021 (94a5a3a) into develop (0589168) will not change coverage.
The diff coverage is n/a.

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##           develop    #6021   +/-   ##
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  Coverage    85.11%   85.11%           
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  Files           55       55           
  Lines         3863     3863           
  Branches       479      479           
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  Hits          3288     3288           
  Misses         463      463           
  Partials       112      112           

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[SaptakS]

As long as #6041 (comment) is addressed in a separate PR, I think this is ready to be merged.

[rmol]

👍 Agree that the label semantics can be improved later, but Orca, at least, reads this current work well.