feat(tableheadercell): add collapsing

[DomiR]

Collapsing is missing from headercells.

[levithomason]

Thanks, we'll also need to update the index.d.ts file in this directory as well as add a test call in TableHeader-test.js.

[levithomason]

Nice, just need a common test now.

[layershifter]

@levithomason Wait a second there. TableHeaderCell is only simple wrapper around TableCell, so collapsing prop will be pass as unhandled.

So, I think it's job for #1169. It's already done in the typings.

[levithomason]

This is true, however, there is also a className and CSS rule for it:

/*--------------
    Collapsing
---------------*/

.ui.table th.collapsing,
.ui.table td.collapsing {
  width: 1px;
  white-space: nowrap;
}

[layershifter]

@levithomason It's not the single property that th has in CSS. I still think that it's not best idea to handle collapsing prop in TableHeaderCell while we handle it too in child TableCell.

[levithomason]

I see what you're saying, the header cell composes the regular cell.

This plays into #1169. There is no documentation visibility with the inheritance here. We could handle this by only adding the propTypes for it, or, pending the babel plugin update for unhandled props, we could spead the cell prop types and update the docs to show "composes" propTypes as well.

[levithomason]

Note that this prop is supported as it is passed to the underlying TableCell. Typings extend the TableCell props as well, so there is support there. Lastly, we're very close to finishing updates to the doc site to show inherited or "composed" propTypes as well, track #1169.

Appreciate the notice and PR here. Closing this PR in favor of those efforts.