Remove kfixedgrid from category search modal

[marcellamaki]

Summary

Fixes #8988

This PR cleans up the CategorySearchModal implementation in several ways.

1. Rather than using KFixedGrid (which does not allow for numCols === 1), it uses KGrid
2. This eliminates the need for some props (that I probably never should have added) also
3. Removes a file that wasn't being used at all! 🆘
4. Changes the display of the CategorySearchModal on the Library page to use FullScreenSidePanel on medium screens, per slack discussion.

References

Most of this refactor should result in no changes to the UI, with the exception of the "medium screen" change (#4):

Reviewer guidance

• Does the category search work at each screen resolution?
• Are there any bugs in the layout (overlapping/squished words, etc.)?

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• 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

[rtibbles]

Was going to leave a comment here about not doing this because strings - but there are no strings in this component, so I'll leave this comment to preempt any such similar comments!

[nucleogenesis]

Code LGTM.

I tested in browser and it looks good!

One thing - the FullScreenSidePanel that contains the sub-menu on mobile (listing all of the options under headings) - should have the fullScreenSidePanelCloseButton prop set to false. In RTL the back arrow and X sit right next to each other.

[marcellamaki]

One thing - the FullScreenSidePanel that contains the sub-menu on mobile (listing all of the options under headings) - should have the fullScreenSidePanelCloseButton prop set to false. In RTL the back arrow and X sit right next to each other.

Good catch. Should be fixed now

[marcellamaki]

Final changes reviewed and ✅ by @radinamatic and @sairina