fix: file storage icons and mobile table styles polish

[sknep]

Changes proposed in this pull request:

• Updates icons to those from mocks for add folder/attachment buttons
• makes button styles consistent with rest of file upload table
• Adds mobile styles for file upload table, similar to USWDS stacking table (https://designsystem.digital.gov/components/table/#responsive-stacked-table-2)
• use isPending rather than isLoading as well as a loading indicator, so that the table doesn't flash an "is empty" message while querying.
• show file storage pagination only when the query returns results, rather than when empty or while querying.

security considerations

• None, front-end only

New icons:

New mobile styles:

[cloud-gov-pages-operations]

🤖 This is an automated code coverage report

Total coverage (lines): 34.08%
Coverage diff: 0% 📈

[apburnes]

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