feat: support []string and ast.Value in ast.InterfaceToValue

[regeda]

Why the changes in this PR are needed?

1. ast.InterfaceToValue walks through json encode/decode for the native ast.Value type. It doesn't make sense as far as the function returns ast.Value.
2. Regarding []string case, it reduces the number of iterations

What are the changes in this PR?

Updates in ast.InterfaceToValue function.

Notes to assist PR review:

Further comments:

[anderseknert]

Seems alright to me. I’m curious though — where do we ever pass this a Value?

[regeda]

Seems alright to me. I’m curious though — where do we ever pass this a Value?

I'm thinking that could be helpful in opa-envoy-plugin where "check request" should be converted into ast.Value.

[anderseknert]

It would be good if you could provide an example where any of these two new paths are hit. I just tried this addition in Regal, and none of them are in that context. But OTOH we don't hit that function much at all since we use an optimized version for that use case. Let's just make sure that this isn't just dead code in any real project integration.

EDIT: heh, I just noticed that we do have []string implemented there, so I guess it is hit after all, just not in OPA in that integration. Still, something to show that would be great.

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