Resolve .worktreeinclude entries and validate that both the source path
stays within the repository root and the destination path stays within
the worktree directory before copying files or creating symlinks.
A malicious .worktreeinclude in a cloned repository could previously
reference paths like "../../etc/passwd" to copy or symlink arbitrary
files from outside the repo into the worktree.
CWE-22: Improper Limitation of a Pathname to a Restricted Directory
