[Perl/perl5] 93af3c: Document various CopFILEfoo functions

[Karl Williamson via perl5-changes]

  Branch: refs/heads/smoke-me/khw-pr_api5
  Home:   https://github.com/Perl/perl5
  Commit: 93af3cc8e0a63e8ad71fe73da425366536035d76
      
https://github.com/Perl/perl5/commit/93af3cc8e0a63e8ad71fe73da425366536035d76
  Author: Karl Williamson <k...@cpan.org>
  Date:   2020-11-22 (Sun, 22 Nov 2020)

  Changed paths:
    M cop.h
    M embed.fnc
    M proto.h

  Log Message:
  -----------
  Document various CopFILEfoo functions