perlfunc: Clarify verbatim table

When I read what was here before this patch, I thought there was a typo,
as there was no entry in column 1 for several rows.  Instead, what was
meant was that the item in column 1 row 1 was supposed to be dittoed
into the following rows.  I used the solution employed in Camel 4,
which is to repeat that item in each row it applies to.
Commit 1735f6f53ca19f99c6e9e39496c486af323ba6a8 started to escape all
back-slashes which breaks case when lexicon translations contain substition
and literals with eval-non-safe characters. E.g.  these translations:

"[_1]foo\\n\n" => "[_1]bar\\n\n",
'[_1]foo\n' => '[_1]aÄa\n',

got doubled back-slashes on the maketext() output.

This patch de-escapes escaped backslashes if the literal is compiled as
function argument.

Fixes RT #120457.