fix: preserve DatePicker tab flow in readOnly mode

[adamalston]

Closes #21152

Preserve DatePicker tab flow in readOnly mode.

Changelog

Changed

• Preserve DatePicker tab flow in readOnly mode.

Testing / Reviewing

yarn test packages/react/src/components/DatePicker/DatePicker-test.js

PR Checklist

As the author of this PR, before marking ready for review, confirm you:

• Reviewed every line of the diff
• Updated documentation and storybook examples
• Wrote passing tests that cover this change
• Addressed any impact on accessibility (a11y)
• Tested for cross-browser consistency
• Validated that this code is ready for review and status checks should pass

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.92%. Comparing base (597001a) to head (84869df).
⚠️ Report is 42 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #22010      +/-   ##
==========================================
+ Coverage   94.90%   94.92%   +0.02%     
==========================================
  Files         541      541              
  Lines       45253    45254       +1     
  Branches     6359     6332      -27     
==========================================
+ Hits        42949    42959      +10     
+ Misses       2172     2163       -9     
  Partials      132      132              

Flag	Coverage Δ
main-packages	89.15% <100.00%> (-0.02%)	⬇️
web-components	97.70% <ø> (ø)

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[heloiselui]

Looks good!

[maradwan26]

LGTM