Need more variants of th-in-row tests

[cookiecrook]

Related to open HTML-AAM ambiguity: https://github.com/w3c/html-aam/issues/523#issuecomment-1894461644_

In addition to or instead of the el-th-in-row test, I think we should split that into a few more:

• el-th-in-thead-row (default columnheader?)
• el-th-in-non-thread-first-row (columnheader if layout table heuristic not triggered? maybe add table and cell borders to avoid the layout table heuristic?)
• el-th-in-non-thread-second-row (rowheader? ditto re: layout table heuristic)
• el-th-in-tbody-row (always rowheader?)
• el-th-in-tfoot-row (always rowheader?)

Originally posted by @cookiecrook in https://github.com/w3c/html-aam/issues/523#issuecomment-1894461644