Validate user names and file paths

Validate user names and file paths

Prevent usage of illegal characters in user names and file paths.
Also, disallow unexpected symlinks in file paths.

This patch contains changes to common source files not applicable
to open-vm-tools.

All files being updated should be consider to have the copyright to
be updated to:

 * Copyright (c) XXXX-2025 Broadcom. All Rights Reserved.
 * The term "Broadcom" refers to Broadcom Inc. and/or its subsidiaries.

The 2025 Broadcom copyright information update is not part of this
patch set to allow the patch to be easily applied to previous
open-vm-tools source releases.