perlop: fix and normalize indentation and alignment

[haarg]

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.

[jkeenan]

This cannot be merged as is. It fails the t/porting/podcheck.t. See end of https://github.com/Perl/perl5/actions/runs/11281442619/job/31376683077?pr=22658 for options on fixing, run make test_porting before re-pushing. Thanks.