relicensing: Rewrite PR "DevicePathToText and DevicePathFromText Protocol"

[nicholasbishop]

See #1521. This rewrites code from supdrewin that we do not have relicensing approval for.

Checklist

• Sensible git history (for example, squash "typo" or "fix" commits). See the Rewriting History guide for help.
• Update the changelog (if necessary)

[phip1611]

General question: Why do we have this type? I think, this can also be a CString16?

Do we at least want to write how it differs from CString16?

[nicholasbishop]

Updated the docstring to clarify. Since this is allocated internally by UEFI, we'd have to do a second memory allocation to copy it to a CString16. (Or alternatively, the CString16 type could be modified to contain either a Vec or a pool allocation, and switch out how it's dropped at the end, but that's probably more complicated than it's worth.) I'm not necessarily opposed to doing something else here, like just accept an extra memory copy, but should probably think about that as part of #1303 since CString16 requires the alloc feature.