Add support for `%r...%r` in `EXPECTF` section

[Bilge]

As documented here:

%r...%r: Any string (…) enclosed between two %r will be treated as a regular expression.

[sebastianbergmann]

Please test #6547 and provide feedback there, thank you.

[Bilge]

Which version(s) will this land in? Since I am currently supporting 10-13 (inclusive), it would need to be available in all these branches for me to make use of it at this time.

[sebastianbergmann]

This will land in PHPUnit 13.x as it is a new feature.