HTMLTable striped doesn't apply correct to row headers

[Firehed]

Environment

• Package version(s): 3.18
• Browser and OS versions: macOS Safari 12

If possible, link to a minimal repro (fork this code sandbox): https://codesandbox.io/s/blueprint-sandbox-stt6c

Steps to reproduce

<HTMLTable striped>
  <thead>...</thead>
  <tbody>
    <tr>
      <th>Some row header</th>
      <td>value</td>
      <!-- ... -->
    </tr>
  </tbody>
</HTMLTable>

Actual behavior

Table striping does not apply to <th> cells in <tbody>, only <td>. While not especially common, it's a valid placement according to the spec, and shown in numerous examples

Interactive tables exhibit similar issues.

Expected behavior

Header cells also receive striping behavior inside the tbody

Possible solution

Looks like it's a relatively minor change to some CSS selectors. However this also seems to impact interactive so a correct fix may be slightly wider-reaching.