Pass rows count to sub-components

[ahmacleod]

Passes the effective row count from each of thead, tbody, tfoot down through the component hierarchy. This count excludes rows that are hidden because their parent is collapsed, reflecting what the user actually sees. It is typically smaller than rows.length.

This can be used in the template to identify when the current row is the bottom rendered row.

Includes docs update and a supporting test.

Example usage:

<EmberTable as |t|>
  <t.head @columns={{columns}} />
  <t.body @rows={{rows}} as |b|>
    <b.row as |r|>
      <r.cell as |cell column row cellMeta columnMeta rowMeta rowsCount|>
        {{#if (eq rowMeta.index 0)}}
          {{!-- custom first row markup --}}
          {{cell}}
        {{else if (lt rowMeta.index (dec rowsCount))}}
          {{!-- middle row markup; `dec` helper is from`ember-composable-helpers` --}}
          {{cell}}
        {{else}}
          {{!-- custom last row markup --}}
          {{cell}}
        {{/if}}
      </r.cell>
    </b.row>
  </t.body>
</EmberTable>

[mixonic]

@ahmacleod can this PR also document the addition?

How do you access the index? Like, can you show an example of the usage?

[ahmacleod]

@ahmacleod can this PR also document the addition?

How do you access the index? Like, can you show an example of the usage?

Docs could definitely use a "how to tell which row this is from the template" section. This ties into #879.

Probably best to extend the "Table Meta Data" section, which currently does not even document the existing rowMeta.index property:

https://opensource.addepar.com/ember-table/docs/guides/main/table-meta-data