Fleet UI: Accessibility button actions, tabbing

[RachelElysia]

Issue

Part 3 of #22606

Description

• Pressing enter when the upload/choose file button is selected will open the file uploader
• Can now tab past the label dropdown on the host page
• Small icon buttons now have styling when tabbing through the app (e.g. filter pill close button on host details page)

TODO: released bug found: When a cancel button is highlighted, pressing enter should cancel not submit the form/modal

Screenrecording

TODO

Checklist for submitter

If some of the following don't apply, delete the relevant line.

• Manual QA for all new/changed functionality

[RachelElysia]

default isn't even a variant. Brand has all the pseudo class styling on it.

[codecov]

Codecov Report

Attention: Patch coverage is 10.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 65.27%. Comparing base (9dbe04d) to head (5755222).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
frontend/components/FileUploader/FileUploader.tsx	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #22916      +/-   ##
==========================================
- Coverage   65.28%   65.27%   -0.01%     
==========================================
  Files        1533     1533              
  Lines      119109   119118       +9     
  Branches     3640     3592      -48     
==========================================
+ Hits        77755    77756       +1     
- Misses      34148    34157       +9     
+ Partials     7206     7205       -1     

Flag	Coverage Δ
frontend	52.02% <10.00%> (-0.04%)	⬇️

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