Forward refs for TableHeader <th>

[tay1orjones]

Summary

In developing column resizing for the data table for Watson IoT PAL, we're unable to set width on <th> elements. We need the ref to these elements to avoid imperatively setting the width from event callbacks (event.target.closest('th') for example).

TableHeader is a function component so we're unable to use the ref attribute on it. We're unable to wrap these with a container without breaking table semantics, and the styling for table headers as well.

Justification

Multiple Watson IoT products require the use of resizable columns.

Specific timeline issues / requests

This work is in progress already. I'd like to get this in ASAP to avoid reimplementing TableHeader ourselves.

Available extra resources

I can submit a PR