Merge branch 'en/dir-traversal'

"git clean" and "git ls-files -i" had confusion around working on
or showing ignored paths inside an ignored directory, which has
been corrected.

* en/dir-traversal:
  dir: introduce readdir_skip_dot_and_dotdot() helper
  dir: update stale description of treat_directory()
  dir: traverse into untracked directories if they may have ignored subfiles
  dir: avoid unnecessary traversal into ignored directory
  t3001, t7300: add testcase showcasing missed directory traversal
  t7300: add testcase showing unnecessary traversal into ignored directory
  ls-files: error out on -i unless -o or -c are specified
  dir: report number of visited directories and paths with trace2
  dir: convert trace calls to trace2 equivalents

diff --cc builtin/clean.c
Simple merge

diff --cc builtin/ls-files.c
Simple merge

diff --cc builtin/worktree.c
Simple merge

diff --cc diff-no-index.c
Simple merge

diff --cc dir.c
Simple merge

diff --cc dir.h
Simple merge

diff --cc entry.c
Simple merge

diff --cc notes-merge.c
Simple merge

diff --cc object-file.c
Simple merge

diff --cc packfile.c
Simple merge