perlop: fix and normalize indentation and alignment

Tabs for alignment don't work well in verbatim sections. The indentation
of the code may be stripped when being displayed, resulting in the tab
alignment not matching the intention. This can currently be seen on
https://metacpan.org/pod/perlop and https://perldoc.perl.org/perlop

Since most of the code uses 4 space indents, normalize all of the
indentation to use 4 spaces.

Author: haarg

pod/perldelta.pod

@@ -143,8 +143,16 @@ XXX Remove this section if F<Porting/corelist-perldelta.pl> did not add any cont
 
 =head1 Documentation
 
-XXX Changes to files in F<pod/> go here. Consider grouping entries by
-file and be sure to link to the appropriate page, e.g. L<perlfunc>.
+=head2 perlop
+
+=over 4
+
+=item *
+
+Normalized alignment of verbatim sections, fixing how they are displayed by
+some Pod viewers that strip indentation.
+
+=back
 
 =head2 New Documentation