remap-lang: allow negative indexing into arrays

[JeanMertz]

given this:

{ "foo": ["bar", "baz"] }

This works:

.foo[0] // "bar"
.foo[1] // "baz"

This does not:

.foo[-1] // "baz"
.foo[-2] // "bar"

There is no technical reason we can't implement this, but the language grammar does not support negative index numbers at the moment.

This was either a deliberate choice to reduce language complexity, or just something we haven't got to yet (I don't know the answer).

Regardless, people seem to run into this limitation (see https://discord.com/channels/742820443487993987/746070591097798688/787115063500472331), so it's worth considering supporting negative indexing in path queries.

[asymmetric]

Is this documented? I couldn't find any mention of negative indexes in the docs.