decoder: Implement validateBody

[dbanck]

Requires #57

Problem Statement

Once we have the schema and the content for a file, we can use a combination of the two for validation.

Proposal

• Implement validateBody
• Raise diagnostics for the following cases
  • extraneous block labels - e.g. variable "one" "two" {
  • missing block labels - e.g. variable {}
  • unknown blocks (top level and within resources)
  • missing required attributes
  • unknown attributes
  • missing required blocks (with set minimum instances of block)
  • too many blocks (with set maximum instances of block)
  • deprecated attributes/blocks (warning)
• Add test cases for all scenarios

User Experience

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Part of hashicorp/vscode-terraform#720