plugin(dirs): Create backup file parent directory

[davidpfarrell]

Fixes #2143

Creates parent directory for dirs plugin backup file.

Description

Adds a mkdir command to create the parent directory for the backup file before trying to touch the file itself.

Motivation and Context

Plugin currently assumes the parent directory exists and causes a failure with error msg during plugin initialization.

How Has This Been Tested?

Tested locally.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• If my change requires a change to the documentation, I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• If I have added a new file, I also added it to clean_files.txt and formatted it using lint_clean_files.sh.
• I have added tests to cover my changes, and all the new and existing tests pass.

[NoahGorny]

Thanks @davidpfarrell !