Fix collapsed border painting on continuation pages.

Three separate defects made a border-collapsed table lose borders when printed across pages:

- SetDamageArea() used nsTableRowFrame::GetNextRow(), which continues into the row group's next-in-flow, so the damage area was a row longer than the page and the iterator ended before the position where accumulated  block-direction segments are flushed.
- IsAfterRepeatedHeader() could never fire, so those segments were not restarted below a repeated header and kept the header's border width.
- BCInlineDirSeg::mAjaCell resolved to the repeated header cell, so the border below it was painted in that cell's style.

Differential Revision: https://phabricator.services.mozilla.com/D322236

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=2033184
gecko-commit: 4b3c7d84b228349f2625795aab3f1478bad528b6
gecko-commit-git: aa2aaac5defa417312dfa80991872e531639fa10
gecko-reviewers: layout-reviewers, emilio