Update copyright message to 2023

[keryell]

Mainly applying this script:

#! /bin/bash
#set -vx

function update_code() {
  file_name="$1"
  # Update the copyright dates and names
  sed -i \
    -e 's/Copyright (c) 2011-2022 The Khronos Group, Inc./Copyright (c) 2011-2023 The Khronos Group, Inc./g' \
    "$file_name"
}

git ls-files | while read -r f ; do
  update_code "$f"
  echo "$f":
  grep -i copyright "$f" | grep -v "2011-2023"
done