Fix #1458, Moves OS_strnlen to public API and adds static analysis co… …mments

[chillfig]

Checklist (Please check before submitting)

• [x] I reviewed the Contributing Guide.
• [x] I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution

• Fixes #1458, Adds a disposition to a line of code in question from static analysis stating why it's safe to keep as-is.

Testing performed Manual inspection

Expected behavior changes N/A

System(s) tested on N/A

Additional context N/A

Third party code N/A

Contributor Info - All information REQUIRED for consideration of pull request Justin Figueroa, Vantage Systems