On arrays, Hashes, and QuantHashes, values from .kv, .values, and .pairs sequences are writable

[JJ]

This is part of the 6.d spec, but so far it's not tested in roast: See Raku/roast#614, so it's for the time being in the limbo. Spun off #2632

Suggestions

Add corresponding documentation when it's tested and thus frozen as spec.