Consolidate selection text formatting.

[rtibbles]

Summary

Description of the change(s) you made

• Elide folders from text when 0 folders selected
• Update all usage of selection text to use common source.
• Update selection text to appear as text box label to maintain text formatting
• Flyby fix of string 'What Levels' to 'Edit Levels'

Manual verification steps performed

1. Selected a single resource
2. Confirmed that 1 resource is displayed only for the selection text.
3. Confirmed that no text displays in the quick edit modals.
4. Select multiple resources or a folder, confirm that appropriate messages display.

Screenshots (if applicable)

References

Fixes #4650

Comments

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Contributor's Checklist

PR process:

• If this is an important user-facing change, PR or related issue the CHANGELOG label been added to this PR. Note: items with this label will be added to the CHANGELOG at a later time
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• The docs label has been added if this introduces a change that needs to be updated in the user docs?
• If any Python requirements have changed, the updated requirements.txt files also included in this PR
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Studio-specifc:

• All user-facing strings are translated properly
• The notranslate class been added to elements that shouldn't be translated by Google Chrome's automatic translation feature (e.g. icons, user-generated text)
• All UI components are LTR and RTL compliant
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Testing:

• Code is clean and well-commented
• Contributor has fully tested the PR manually
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• Critical and brittle code paths are covered by unit tests

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Reviewer's Checklist

This section is for reviewers to fill out.

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[marcellamaki]

looks good. code changes were very clear to follow, and manual QA checks out

[radinamatic]

Manual QA on the unstable branch confirms the fix.