decoder: validate required attributes more selectively

[radeksimko]

Depends on hashicorp/hcl-lang#341

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Summary

This patch provides us a way to dampen the impact of hashicorp/vscode-terraform#1616 Note that it does not really solve the issue entirely since even resources and data sources may in theory have various dynamic defaults for attributes which are also marked as required.

We could've used schemacontext.WithUnknownSchema() here to indicate "unknown-ness" of the provider schema. This would currently achieve the same effect but it would mix up the abstraction layers (currently it's only hcl-lang which attaches the ctx value via schemacontext.WithUnknownSchema and then its own validators read it) and it would IMHO lead to abuse of that concept of "unknown-ness". By using a separate context value we can mostly isolate the handling of this edge case to the LS codebase as it is indeed a "Terraform schema edge case" and not necessarily HCL's problem or problem that will generally exist in other HCL-based languages.

Another new (more generic) upstream context value "block nesting level" is also leveraged here to ensure that we don't end up interpreting any block called provider (e.g. inside of resource or data blocks) as the actual provider block we mean.

UX Before

UX After

[dbanck]

👍

Feel free to merge after bumping hcl-lang

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