Change emu-table to use CSS grid to make them less verbose

Currently a table looks like:

<emu-table id="table-2" caption="Attributes of a Data Property">
    <table>
    <tbody>
    <tr>
        <th>
        Attribute Name
        </th>
        <th>
        Value Domain
        </th>
        <th>
        Description
        </th>
    </tr>
    <tr>
        <td>
        [[Value]]
        </td>
        <td>
        Any ECMAScript language type
        </td>
        <td>
        The value retrieved by a get access of the property.
        </td>
    </tr>
    <tr>
        <td>
        [[Writable]]
        </td>
        <td>
        Boolean
        </td>
        <td>
        If *false*, attempts by ECMAScript code to change the property's [[Value]] attribute using [[Set]] will not succeed.
        </td>
    </tr>
    <tr>
        <td>
        [[Enumerable]]
        </td>
        <td>
        Boolean
        </td>
        <td>
        If *true*, the property will be enumerated by a for-in enumeration (see <emu-xref href="#sec-for-in-and-for-of-statements"></emu-xref>). Otherwise, the property is said to be non-enumerable.
        </td>
    </tr>
    <tr>
        <td>
        [[Configurable]]
        </td>
        <td>
        Boolean
        </td>
        <td>
        If *false*, attempts to delete the property, change the property to be an accessor property, or change its attributes (other than [[Value]], or changing [[Writable]] to *false*) will fail.
        </td>
    </tr>
    </tbody>
    </table>
</emu-table>

A CSS grid would look like:

<emu-table id="table-2" caption="Attributes of a Data Property">
  <emu-th>Attribute Name</emu-th>
  <emu-th>Value Domain</emu-th>
  <emu-th>Description</emu-th>

  <emu-td>[[Value]]</emu-td>
  <emu-td>Any ECMAScript language type</emu-td>
  <emu-td>The value retrieved by a get access of the property.</emu-td>

  <emu-td>[[Writable]]</emu-td>
  <emu-td>Boolean</emu-td>
  <emu-td>If *false*, attempts by ECMAScript code to change the property's [[Value]] attribute using [[Set]] will not succeed.</emu-td>

  <emu-td>[[Enumerable]]</emu-td>
  <emu-td>Boolean</emu-td>
  <emu-td>If *true*, the property will be enumerated by a for-in enumeration (see <emu-xref href="#sec-for-in-and-for-of-statements"></emu-xref>). Otherwise, the property is said to be non-enumerable.</emu-td>

  <emu-td>[[Configurable]]</emu-td>
  <emu-td>Boolean</emu-td>
  <emu-td>If *false*, attempts to delete the property, change the property to be an accessor property, or change its attributes (other than [[Value]], or changing [[Writable]] to *false*) will fail.</emu-td>
</emu-table>

The <emu-th> would define the number of columns.

I've been adding a bunch of stuff to tables and this would make things look clean.

The issue names no files or tests. Start by locating the emu-table handling and the styles that render its contents, then verify how emu-th and emu-td can define the columns. Done means the compact syntax in the example renders the same table using CSS grid.