feat: add keyboard accessibility for timepicker

[asajjad2]

What are the relevant tickets?

#9097

Description (What does it do?)

Time fields in Schedule settings rely on react-datepicker’s time-only popover, which only responds to mouse input. ArrowUp/ArrowDown do nothing, so keyboard and screen-reader users can’t adjust the time.

This PR intercept ArrowUp/ArrowDown in DatepickerControl when it’s used as a time picker, parse the current value, and advance/rewind by 30-minute steps. Let react-datepicker update the highlighted entry and scroll the popover into view.

Screencast

Screen.Recording.2025-11-11.at.3.38.55.PM.mov

How can this be tested?

1. On schedule page, focus a time field and press ArrowDown/ArrowUp—time should shift ±30 minutes, and the highlighted row stays visible.
2. Verify mouse interactions still work as before.

[openedx-webhooks]

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[codecov]

Codecov Report

❌ Patch coverage is 82.69231% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.72%. Comparing base (3089d0b) to head (3b6bcc3).
⚠️ Report is 1227 commits behind head on master.

Files with missing lines	Patch %	Lines
...c/generic/datepicker-control/DatepickerControl.jsx	82.69%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2613      +/-   ##
==========================================
+ Coverage   93.02%   94.72%   +1.69%     
==========================================
  Files         756     1233     +477     
  Lines       13708    27759   +14051     
  Branches     2961     6280    +3319     
==========================================
+ Hits        12752    26294   +13542     
- Misses        920     1390     +470     
- Partials       36       75      +39     

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[bradenmacdonald]

Thanks, this looks nice! Please let me know when it's ready for review.

Also, will this work with v8 ? #2572
Ideally we could add this functionality and do the version bump at the same time.