[perl #130117] [REGEX] :r does not prevent backtracking (say ‘abcz’ ~~ /:r [‘a’ || ‘abc’ ] ‘z’ /)

[Sam S. via RT]

Relevant:

https://rt.perl.org/Ticket/Display.html?id=123934#txn-1401917

In short, `||` alternations don't respect `:` in Rakudo, whereas `|` 
alternations (and other atoms such as quantifiers) do respect it.

Simpler test-case:

    ➜  say "ab" ~~ / [ "ab" | "a" ]: "b" /;
    Nil

    ➜  say "ab" ~~ / [ "ab" || "a" ]: "b" /;
    ｢ab｣

(Remember that `:ratchet` simply adds `:` to every atom.)