Add clang-format shell script (OSGeo#2732)

The clang-format shell script replaces the grass_indent.sh and
grass_indent_ALL.sh scripts, which are both hereby removed.

utils/grass_clang_format.sh

@@ -0,0 +1,74 @@
+#!/bin/sh
+set -eu
+
+###############################################################################
+# Format source code according to GRASS GIS submitting rules
+#
+# Dependencies:
+#    clang-format
+#      (most easily available with e.g.:
+#      `python -m pip install 'clang-format==15.0.6’`)
+#
+# Author(s):
+#    Nicklas Larsson
+#
+# Usage:
+#    If you have "clang-format" in PATH, execute for complete source formatting:
+#      ./utils/grass_clang_format.sh
+#
+#    Setting 'GRASS_CLANG_FORMAT' to explicitly set clang-format version:
+#      GRASS_CLANG_FORMAT="clang-format-15" ./utils/grass_clang_format.sh
+#
+#    It is also possible to format the content in a (one) given directory:
+#      ./utils/grass_clang_format.sh ./lib/raster
+#
+# COPYRIGHT: (C) 2023 by the GRASS Development Team
+#
+#            This program is free software under the GNU General Public
+#            License (>=v2). Read the file COPYING that comes with GRASS
+#            for details.
+#
+###############################################################################
+
+# Required clang-format version
+req_cf_v="15"
+
+# No need to continue if the .clang-format file isn't found
+if [ ! -f .clang-format ]; then
+    echo "Error: could not find the .clang-format file. Is the GRASS source"
+    echo  "  top directory your working directory?"
+    exit 1
+fi
+
+# If set, use env variable GRASS_CLANG_FORMAT for clang-format
+if [ -z ${GRASS_CLANG_FORMAT+x} ]; then
+    fmt="clang-format"
+else
+    fmt="${GRASS_CLANG_FORMAT}"
+fi
+
+if ! (${fmt} --version >/dev/null); then
+    echo "clang-format not available."
+    exit 1
+fi
+
+clang_version_full=$(${fmt} --version)
+clang_version=$(echo "${clang_version_full}" | cut -f3 -d" " | cut -f1 -d".")
+if [ "${clang_version}" -lt "${req_cf_v}" ]; then
+    echo "Error: ${clang_version_full}"
+    echo "  is used, but version ${req_cf_v} or newer is required."
+    echo "  Consider setting the global variable GRASS_CLANG_FORMAT to"
+    echo "  the clang-format version needed."
+    exit 1
+fi
+
+# One argument, a directory path is allowed
+if [ "$#" -eq 1 ] && [ -d "$1" ]; then
+    dir="$1"
+else
+    dir="."
+fi
+
+find "${dir}" -type f \
+    '(' -iname '*.c' -o -iname '*.cpp' -o -iname '*.h' -o -iname '*.hpp' ')' \
+        -exec "${fmt}" -i '{}' +