fix: Robust symlink handling in installer

[edcet]

This PR addresses issues in the Dorothy installer (commands/dorothy) related to symbolic link creation, specifically:

1. Identical Source/Destination Paths: Prevents "Directory not empty" errors when the installer attempts to create a symlink where the source and destination paths are identical (e.g., ln -s /path/to/dir /path/to/dir). This often occurs with --no-xdg installations.
2. Broken Symlinks at Target: Ensures that if an identical path scenario is encountered and the target is a broken symlink, the broken symlink is removed.
3. Missing Parent Directories: Ensures parent directories are created before attempting mv or ln operations within relocation functions, preventing "No such file or directory" errors for __fs_realpath or mv.

Problem Details:

• The relocate_then_symlink_if_necessary function could fail if $symlink and $destination were the same, as ln -sfF cannot replace a non-empty directory with a symlink to itself.
• If $symlink was a broken symlink and identical to $destination, the broken link wasn't cleaned up.
• The relocate_if_necessary function could fail if parent directories for $destination didn't exist before mv or __fs_realpath calls.

Fixes Implemented:

1. In relocate_then_symlink_if_necessary:
   • Added a check: if $symlink and $destination are identical, it now first removes $symlink if it's a broken symlink, then skips the ln operation.
   • Ensures parent directories for $symlink and $destination are created using mkdir -p at the beginning of the function.
2. In relocate_if_necessary:
   • Ensures parent directories for $source and $destination are created using mkdir -p at the beginning of the function.

Testing:
Verified on macOS:

• Installer completes successfully when DOROTHY is set to an existing target directory (testing identical path fix).
• Installer correctly handles and cleans up broken symlinks when they are also the target of an identical-path symlink operation.
• Relocation logic correctly creates necessary parent directories, avoiding grealpath errors.

[balupton]

Not sure just deleting dorothy is the solution here...

Is this fixed already on the latest dev branch, which is dev/devilbird ? Note that devilbird changes a lot, so you may have breaks/incompatibilities with your user config, it is still under dev so a lot is still broken - however, I recall I may have rewritten the broken functionality already.

[edcet]

Apologies for the noise.

[balupton]

#281 is now merged which fixes this