perl #77654: quotemeta quotes non-ASCII consistently

perl #77654: quotemeta quotes non-ASCII consistently

As described in the pod changes in this commit, this changes quotemeta()
to consistenly quote non-ASCII characters when used under
unicode_strings.  The behavior is changed for these and UTF-8 encoded
strings to more closely align with Unicode's recommendations.

The end result is that we *could* at some future point start using other
characters as metacharacters than the 12 we do now.