Recursively list Android image contents.

Relies on debugfs utility to inspect image contents.
The output looks something like this:
```
./
./app/
./app/Calendar/
./app/Calendar/Calendar.apk
```

Test: manual
Change-Id: Ia05f4e857dfd28ac76ac2b450b08f5cf5577d21f

scripts/Android.bp

@@ -188,3 +188,8 @@ python_binary_host {
         "get_clang_version.py",
     ],
 }
+
+sh_binary_host {
+    name: "list_image",
+    src: "list_image.sh",
+}

scripts/list_image.sh

@@ -0,0 +1,51 @@
+#! /bin/bash
+
+# Recursively list Android image directory.
+set -eu
+set -o pipefail
+
+function die() { format=$1; shift; printf "$format\n" "$@"; exit 1; }
+
+# Figure out the filer utility.
+declare filer=
+[[ -z "${ANDROID_HOST_OUT:-}" ]] || filer=${ANDROID_HOST_OUT}/bin/debugfs_static
+if [[ "${1:-}" =~ --debugfs_path=(.*) ]]; then
+  filer=${BASH_REMATCH[1]}
+  shift
+fi
+if [[ -z "${filer:-}" ]]; then
+  maybefiler="$(dirname $0)/debugfs_static"
+  [[ ! -x "$maybefiler" ]] || filer="$maybefiler"
+fi
+
+(( $# >0 )) || die "%s [--debugfs_path=<path>] IMAGE" "$0"
+
+[[ -n "${filer:-}" ]] || die "cannot locate 'debugfs' executable: \
+--debugfs_path= is missing, ANDROID_HOST_OUT is not set, \
+and 'debugfs_static' is not colocated with this script"
+declare -r image="$1"
+
+function dolevel() {
+  printf "%s/\n" "$1"
+  # Each line of the file output consists of 6 fields separated with '/'.
+  # The second one contains the file's attributes, and the fifth its name.
+  $filer -R "ls -l -p $1" "$image" 2>/dev/null |\
+    sed -nr 's|^/.*/(.*)/.*/.*/(.+)/.*/$|\2 \1|p' | LANG=C sort | \
+  while read name attr; do
+    [[ "$name" != '.' && "$name" != '..' ]] || continue
+    path="$1/$name"
+    # If the second char of the attributes is '4', it is a directory.
+    if [[ $attr =~ ^.4 ]]; then
+      dolevel "$path"
+    else
+      printf "%s\n" "$path"
+    fi
+  done
+}
+
+# The filer always prints its version on stderr, so we are going
+# to redirect it to the bit bucket. On the other hand, the filer's
+# return code on error is still 0. Let's run it once to without
+# redirecting stderr to see that there is at least one entry.
+$filer -R "ls -l -p" "$image" | grep -q -m1 -P '^/.*/.*/.*/.*/.+/.*/$'
+dolevel .