td, th, tr allowances when within a table #38

when used within a role=table, grid, treegrid the td, tr, and th elements should not be allowed any explicitly set role, as that would break the a11y mappings of the table, grid or treegrid.
td in role=table
td in role=grid
td in role=treegrid

tr in role=table
tr in role=grid
tr in role=treegrid

th in role=table
th in role=grid
th in role=treegrid

expectations:

• if a <td>'s ancestor table element has role=table, grid or treegrid - then no allowed role.
• if a <th>'s ancestor table element has role=table, grid or treegrid - then no allowed role.
• if a <tr>'s ancestor table element has role=table, grid or treegrid - then no allowed role.
• if any use of cell, gridcell, row, rowheader, columnheader are found on these elements - then those should produce warnings as being unnecessary

if a td, tr, or th are used within a table with no set role, thus it should be an implicit role=table (regardless of what browser heuristics may do) - then no allowed role
td within a table testcase
th within a table testcase
tr within a table testcase

If td, tr, or th are used within a table where it's role is overwritten by a role not mentioned above (e.g., role=none, article, etc), then these elements can continue to allow any role. the checker already meets this expectation