Support for <tfoot> in <HTMLTable>

[saruman1234]

Environment

• Package version(s): @blueprintjs/core@3.41.0

Feature request

Support using <tfoot> for table footer inside <HTMLTable> (along with bordered, striped, interactive variants) by adding the missing borders and/or background color.

• There are currently styles for <thead>, but not <tfoot>.
• This would be useful for aggregate/summary values like column totals.
• Can be done as custom CSS, but feels like something that could be supported by the package.

Example of current appearance (missing both vertical and horizontal borders)

Example TSX

import React from "react";
import { HTMLTable } from "@blueprintjs/core";

const Example = () => {
  return (
    <HTMLTable bordered striped>
      <thead>
        <tr>
          <th>Item</th>
          <th>Color</th>
          <th>Amount</th>
        </tr>
      </thead>
      <tbody>
        <tr>
          <td>Laptop</td>
          <td>Silver</td>
          <td>$125</td>
        </tr>
        <tr>
          <td>Phone</td>
          <td>Black</td>
          <td>$225</td>
        </tr>
      </tbody>
      <tfoot>
        <tr>
          <td colSpan={2}></td>
          <td>$350</td>
        </tr>
      </tfoot>
    </HTMLTable>
  );
};

export default Example;