TableSorter: Fix column order when collecting headers

Before we did a 'lazy' explode of the columns and rows, a side
effect of this was that a header (A) on a row >= 1 would get a
headerIndex that was higher than that of the header (B) with a
rowspan, that would visually be after header (A).

This caused headers to control the wrong column

Bug: 53211
Change-Id: I852d2860951a4e48f7fb2f6bf8c26b986af3e727
Merge "TableSorter: Fix column order when collecting headers"