Merge branch 'sc/wt-status-avoid-quadratic-insertion' into next

The enumeration of untracked and ignored files in 'git status' has
been optimized by avoiding quadratic complexity insertion into string
lists, reducing the construction cost from O(n^2) to O(n log n).

* sc/wt-status-avoid-quadratic-insertion:
  wt-status: avoid repeated insertion for untracked paths