[28] JEP 542: PEM Encodings of Cryptographic Objects

ref: https://openjdk.org/jeps/542

Summary
Introduce an API for encoding objects that represent cryptographic keys, certificates, and certificate revocation lists into the widely-used [Privacy-Enhanced Mail](https://en.wikipedia.org/wiki/Privacy-Enhanced_Mail) (PEM) transport format, and for decoding from that format back into objects.

ref #5108 for an earlier avatar

Investigate.

Read JEP 542 and the referenced earlier avatar issue #5108 first. No files, tests, or entry points are named, so identify whether Eclipse JDT Core should support the proposed PEM API and document a concrete scope or follow-up; done means the investigation has produced an agreed implementation target.

Written by the indexing model from the issue text.