Support for-in-if expressions

[radeksimko]

Background

Terraform supports for expressions. For example:

• [for s in var.list : upper(s)]
• [for k, v in var.map : length(k) + length(v)]
• {for s in var.list : s => upper(s)}
• [for s in var.list : upper(s) if s != ""]

Language server currently doesn't support these, which means that e.g.

• LS doesn't suggest for while completing the inside of a list/set (within square brackets [ ])
• LS doesn't provide completion for the in part of a for expression, e.g. [for s in _HERE_, nor the result after :, nor after if clause
• LS doesn't display any details (such as type or description) on hover over for expressions
• LS doesn't highlight valid expressions surrounding for/in/if via semantic tokens

Proposal

Completion

TODO

Hover

TODO

Semantic Tokens

TODO

[github-actions]

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