[Perl/perl5] 56edaf: perlapi: Document hv_existss, hv_fetchs

[Karl Williamson via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 56edaf7ac8a3977bc296e458ccabb136b08310b5
      
https://github.com/Perl/perl5/commit/56edaf7ac8a3977bc296e458ccabb136b08310b5
  Author: Karl Williamson <k...@cpan.org>
  Date:   2024-02-05 (Mon, 05 Feb 2024)

  Changed paths:
    M hv.c

  Log Message:
  -----------
  perlapi: Document hv_existss, hv_fetchs

And change the pod of related functions for consistency.