+test (r)index for lists of overlapping needles (Rakudo issue #6104)

[schultzdavid]

Wrapping up Rakudo issue 6104, add some tests for index & rindex of the form

"ab".index: <b ab>

(this line of code having wrongly yielded 1 until lizmat's recent fix 1d991f9).

The tests are

• mostly targeted tests for specific "overlap configurations", and
• one hodgepodge test at the end to catch other cases of wrong behavior.

[lizmat]

Thanks!