Fixes #1118

This commit fixes a regression introduced in 70968d46.

- Fixes an off-by-one error when navigating by rows, caused by treating
  the table header as a row. The table header now has the header
  accessibility role.
- Fixes a bug where reordering table columns would cause the table to
  become inaccessible.
- Fixes a bug where the screen reader would try to navigate hidden table
  columns.
- Fixes an issue where moving the VoiceOver cursor to a partially hidden
  cell would cause the focus to move to the table itself, rather than to
  the cell.

The bug was triggered on Monterey where a pressure of 1 is reported
while a mouse button is being held down. This caused an extra drag
event being triggered between mouse down and up events, even if no
movement occurred.

This restores the behaviour of TreeViews with custom item components prior to ec990202

This fixes warnings that are emitted when building with the `-analyze`
flag enabled.