decoder: Add support for parenthesis on LHS (map keys & attribute names)

[radeksimko]

Depends on:

• decoder: Add support for parenthesis on RHS #366

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This enables support for interpolated map keys and object attribute names,. Since this is enabled by parenthesis it is closely related to that linked PR which adds support for that expression type.

In other words this enables parenthesis support on the LHS (left hand side).

Example:

map_attr = {
  (var.keyname) = "foo"
}

Implementation Notes

This does not enable equivalent support inside of inferred maps/objects, such as in the context of Terraform's locals. This is currently tracked under hashicorp/terraform-ls#1586

It originally started out as "hidden implementation detail" of decoder (the decision whether interpolation is allowed was originally just implied by AnyExpression{} until I realised that we still use schema.Map{} and schema.Object{} in contexts where we expect interpolation, including interpolated keys, so I had to walk it back and make it a more 1st class feature of the schema, for better or worse.

For that reason, this will also require some changes downstream:

• schema: Enable interpolated map keys and object attribute names terraform-schema#316

UX Examples

Completion

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Semantic Tokens

Reference Origins

[dbanck]

LGTM! Just two small nits