schema: Add custom token modifiers

[radeksimko]

Related to hashicorp/vscode-terraform#958

---

This is admittedly somewhat boring PR, just updating all the different parts of schema to make use of the new changes introduced in hashicorp/hcl-lang#106 and essentially allow Language Server to use the hcl-lang decoder along with this updated schema to report these custom modifiers for relevant parts of configuration.

[radeksimko]

This is probably the most important part of the PR.

It's worth noting that these modifiers - similar to token types - share a global namespace (at least in VSCode) - and so should be prefixed. There doesn't seem to be a way of scoping token modifiers or types to just a single language ID in VSCode.

Two minor changes I'm thinking about here is possibly terraform-name => terraform-label-name & terraform-type => terraform-label-type, just to make it more obvious these are used in the context of labels. However it may look kinda awkward/unnecessary when used in the VSCode theme addressing scheme, such as

{
    "semanticTokenColors": {
      "hcl-blockLabel.terraform-resource.terraform-type": "#ff0011",
      "hcl-blockLabel.terraform-resource.terraform-name": "#ff0011"
    }
}

vs

{
    "semanticTokenColors": {
      "hcl-blockLabel.terraform-resource.terraform-label-type": "#ff0011",
      "hcl-blockLabel.terraform-resource.terraform-label-name": "#ff0011"
    }
}

[dbanck]

I would stick with terraform-type and terraform-type because, as you said, the other choices look kinda unnecessary verbose.

[dbanck]

👍