feat: Add UAP buttons to resizable table column headers

[avinashbot]

Description

Screen.Recording.2025-09-26.at.11.53.37.mov

Related links, issue #, if available: AWSUI-60549

API changes

This PR adds a new property to the table's ariaLabels property:

   interface AriaLabels {
     ...
+   resizerTooltipText?: string;
     ...
   }

Let's consider the 👍s on this as approval for the API changes.

How has this been tested?

• Relying on existing tests for dragging behavior, adding new tests for the UAPs. Dry-run build ID: 7533427216.
• Visual changes tested in jowejowe's pipeline - noting unexpected
• Bug bash: zb3AAbRNaDaY

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

---

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[codecov]

Codecov Report

❌ Patch coverage is 97.14286% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.15%. Comparing base (46bf2fc) to head (e701a6b).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/table/resizer/index.tsx	96.52%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3892      +/-   ##
==========================================
- Coverage   97.16%   97.15%   -0.02%     
==========================================
  Files         850      850              
  Lines       24785    24872      +87     
  Branches     8735     8761      +26     
==========================================
+ Hits        24082    24164      +82     
+ Misses        696      659      -37     
- Partials        7       49      +42     

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[avinashbot]

Making a distinction between isPointerDown and isDragging because we want to support a "click" interaction. Currently, a mousedown starts a drag and a mouseup ends it, which means, if you click the divider slightly off center, it jumps before showing the buttons, which looks really janky. So with this, the column widths are only adjusted when the mouse starts moving.

[avinashbot]

We added both isDragging and isPointerDown to our dependencies in the useEffect above, which means this timer get destroyed and created twice. Not a problem for real users, but this really screws with tests (since jest's time-skipping timer methods won't work if the timer is recreated).

[avinashbot]

Previously, the drag handle wrapper had three nested divs I had to contend with styling them all. Since two of those divs only exist for event handling/capture reasons, I can safely just set them to display: contents and only worry about styling one div.

[avinashbot]

Not sure why this behavior was there before, but clicking on the drag handle doesn't move focus to it. But now it does, like any regular button. Helps with simplifying the UAP logic, and is also nicer because you can switch between drag and keyboard.