Dragging a terminal tab within the same Terminals view now reorders it
to the drop position, matching the drag-to-reorder behavior of editor
and view tabs. The drop within the same view was previously rejected.

Only drops on the tab strip reorder, either onto another tab or onto
the empty space next to the tabs (which targets the last position).
Drops on the terminal content area are still rejected. The transfer
state is cleared when the drag finishes so no stale tab item is kept
referenced.

The reorder uses the new CTabFolder.moveItem(int, int) API, so the live
terminal control stays attached and no longer has to be recreated. The
existing cross-view move (which transfers a terminal to a different
Terminals view) is unchanged, as it still requires re-parenting.

Requires SWT 3.135.

Fixes https://github.com/eclipse-platform/eclipse.platform/issues/2679