Bug 1730442 - part 7: Rewrite `HTMLEditor::InsertTableRowsWithTransaction()`...

Bug 1730442 - part 7: Rewrite `HTMLEditor::InsertTableRowsWithTransaction()` to collect any cell information before touching the DOM tree r=m_kato

This patch also makes it inserts table rows immediately after the previous
row element of the found reference row element to make it insert new table
rows immediately after there when inserting position is "after".  Typically,
it's the parent `<tr>` element of `aCellElement`.  Therefore, this approach
can preserve text nodes immediately after it which was intentionally inserted
by the web apps.

Differential Revision: https://phabricator.services.mozilla.com/D146365