[framework]Add semantics role to table rows. (#163337)
**1. framework side:**
This PR Create semantics node for rows in table's
`assembleSemanticsNode` function.
**2. web side:**
I tested on my mac, and i need to remove the
`<flt-semantics-container>` between table and row, row and cell to
traverse inside table, removing those transfom intermediate containers
on web will be a bit of hassle and will be in another separate PR.
For example this code can only announce table but can’t get into cells.
```
<flt-semantics id="flt-semantic-node-4" role="table" style="position: absolute; overflow: visible; width: 751px; height: 56px; transform-origin: 0px 0px 0px; transform: matrix(1, 0, 0, 1, 0, 56); pointer-events: none; z-index: 1;">
<flt-semantics-container style="position: absolute; pointer-events: none; top: 0px; left: 0px;">
<flt-semantics id="flt-semantic-node-6" role="row" style="position: absolute; overflow: visible; width: 751px; height: 56px; top: 0px; left: 0px; pointer-events: none;">
<flt-semantics-container style="position: absolute; pointer-events: none; top: 0px; left: 0px;">
<flt-semantics id="flt-semantic-node-5" role="columnheader" aria-label="Name" style="position: absolute; overflow: visible; width: 751px; height: 56px; top: 0px; left: 0px; pointer-events: all;"></flt-semantics>
</flt-semantics-container>
</flt-semantics>
</flt-semantics-container>
</flt-semantics>
```
If I removed the in between `</flt-semantics-container>`, the code come
```
<flt-semantics id="flt-semantic-node-4" role="table" style="position: absolute; overflow: visible; width: 751px; height: 56px; transform-origin: 0px 0px 0px; transform: matrix(1, 0, 0, 1, 0, 56); pointer-events: none; z-index: 1;">
<flt-semantics id="flt-semantic-node-6" role="row" style="position: absolute; overflow: visible; width: 751px; height: 56px; top: 0px; left: 0px; pointer-events: none;">
<flt-semantics id="flt-semantic-node-5" role="columnheader" aria-label="Name" style="position: absolute; overflow: visible; width: 751px; height: 56px; top: 0px; left: 0px; pointer-events: all;"></flt-semantics>
</flt-semantics>
</flt-semantics>
```
And I can get into table cells.
**3. Other aria-attributes:**
[aria-colcount](https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Attributes/aria-colcount) ,[aria-rowcount](https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Attributes/aria-rowcount)
[aria-colindex](https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Attributes/aria-colindex)
[aria-rowindex](https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Attributes/aria-rowindex)
* theres attributes are only needed if some rows and columns are hidden
in the Dom tree. havn't added them yet
aria-rowspan , aria-colspan :
*we currently don't support row span and col span in our widgets.
related issue: https://github.com/flutter/flutter/issues/21594
related: https://github.com/flutter/flutter/pull/162339
issue: https://github.com/flutter/flutter/issues/45205
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