fix(version): only apply prettier if it was explicitly installed

[JamesHenry]

Description

Only invoke prettier on changed files if the user has explicitly listed it in their root package.json.

Motivation and Context

It is theoretically possible that a user could end up with a copy of prettier in their node_modules despite not being a direct user of it. This situation might cause unwanted formatting changes to their files when running lerna version.

Nobody has explicitly reported this case to us, but it is theoretically possible and we might have seen it be indirectly reported via a community blog post.

How Has This Been Tested?

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)
• Chore (change that has absolutely no effect on users)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.