SubstituteAndReturn: contextual and chained substitute

The plugin does not currently support substitution with the `r` flag

1. that uses `$_`, e.g.,
```perl
map { s/foo/bar/r } @list
```
which does not change the input

2. and chained substitution, e.g.,

```perl
$foo =~ s/foo/bar/gr =~ s/(bar)+/baz/gr
```
which gives
```perl
(map { (my $__B_001 = $_) =~ s/foo/bar/g; $__B_001 } $foo)[0] =~ s/(bar)+/baz/gr
```
